Thanks @gabimoskowitz for the list request! I was actually working on a similar list but abandon it for various reasons. Most people should probably have a lot of this already in their kitchen.
  1. Mixing bowls
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    Various sizes. Big to small. Get nesting ones for easier storage. Glass and metal. Ceramic is nice but heavy. I skip the plastic bowls because they are hard to clean afterwards. They always feel greasy to me no matter how much I wash them. Also I'm not a fan of plastic in general.
  2. Rolling pin
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    Get a rolling pin your comfortable with. I like my French tapered one. It's one piece, with tapered ends. I get more control over the roll. But others like straight edge ones or ones with ball bearings inside for a smoother roll. Just find one that works for you.
  3. Selection of large spatulas
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    You don't need huge ones but big ones are nice to have. They properly scrape your bowls to make sure it completely mixed with no patches of flour or wet ingredients. And they are perfect for folding in egg whites and whipped cream into batter and frosting. I have way too many of them. But I use them all.
  4. Balloon whisk
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    Whisks come on all sorts of sizes and shapes. I have the kind that have the balls at the end. I have big huge whisks. There are even flat whisks. But the one I use the most is a standard ballon whisk about 11-inches in length. I use it not only to beat eggs and whisk in liquids but to stir together dry ingredients, evenly blending them. Way easier and faster than "sifting" them all together.
  5. A kitchen scale
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    Every pro baker will tell you that a kitchen scale is the best and easiest way to get consistent results. Flour can weigh anywhere from 125 g to 160 g per cup in how you measure. That's a huge difference if the recipe calls for 3 cups of flour. Get a scale that tares (will return to zero when you press the tare button) and that does grams. Bonus, less stuff to clean. Just dump in ingredients, tare, add the next ingredient. No more washing those measuring cups.
  6. Flat parchment paper
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    This is the workhorse of the baker's kitchen. Actually any kitchen. Use it to line baking pans & sheets. Cut out circles to place on top of slow cooking dishes on the stovetop (called a cartouche). Wrap leftover cheese in it. It's exceedingly versatile. Flat sheets are always preferred because the rolled sheets curl up when you use them (so annoying). Go to a kitchen supply place (like Surfas in LA) and buy a package of flat sheets. It'll last you forever. You can store them top of the fridge.
  7. Silicon mat
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    I love my parchment paper but I also use my silicon baking mat (or silpat) for baking cookies a lot. It's basically like a reusable parchment paper sheet. Totally worth the money. Easy to clean up. Protects my baking sheets.
  8. Microplane grater
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    They did an interview with famous chefs a few years ago asking them what "new" equipment changed their lives. This one got mentioned a lot! This is by far the easiest way to zest citrus or grate chocolate. It also great with grating hard cheese like Parmesan or flavoring your vinaigrettes. Just use it to grate a shallot, garlic clove or ginger into your oil & vinegar emulsion. Instant fancy vinaigrette. Totally versatile piece of equipment for under $15.
  9. Oven thermometer
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    Most built-in oven thermometers go out of whack once you've had the oven for awhile. Even brand new ovens are often wrong by up to 50 degrees from the get go. This is why your cookies and brownies burn or take forever to bake even when you follow the instructions exactly. An oven thermometer will give you a sense of how off your oven is and how to adjust it if necessary.
  10. Various baking pans
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    This should be a given but having the right size pan is important. If you only have 9-inch round cake pans and the recipe calls for 8-inch round, you're going to end up with thin flat layers of cake that cake faster. Recipes are designed specifically for the pan stated. So having a variety of them is good. Try to get lighter colored pans. The dark colored ones get hotter and your edges will brown faster.
  11. Half sheet pans
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    I specifically calls this out because they are super versatile. Buy the heavy duty commercial grade half sheet pans, which are rimmed baking sheets that fit into nearly all home ovens. I used them nearly exclusively for baking cookies as well as roasting vegetables and spatchcock chicken. You can get them fairly cheap at a restaurant supply shop it sometimes I find them at Marshall's or TJ Maxx.
  12. Wire cooling racks
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    So necessary for cooling all your baked goods. Get a couple of round ones for cakes and a couple of square or rectangles ones for cookies.
  13. Glass measuring cups
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    For liquid measurement. Don't use a dry measuring cup. It won't give you accurate measurements for liquids.
  14. Dry measuring cups/spoons
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    Actually you probably already have these and if you have a scale you won't use them often. But the measuring spoons are used pretty frequently in my kitchen. I don't trust my scale for small measurement amounts of two grams and such. So I just use the teaspoon/tablespoons instead.
  15. Pastry brush
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    But a couple of cheap bristle one. Don't get a silicon one, they don't hold liquid well. Use it to brush off flour, brush on egg washes, brush away crumbs. Super cheap, like $2.
  16. Sieve
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    Use it to dust powdered sugar, sift dry clumpy ingredients like powdered sugar or almond flour, strain liquids and custards/curds. Totally versatile. Get a fine mesh one and a larger mesh one.
  17. Stand mixer
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    This is probably the most expensive thing on the list and you shouldn't buy one of you don't really bake a lot. I got by with a hand mixer for years but once I upgraded there was no going back. Nowadays a large number of recipes are designed with the stand mixer in mind because it's easier and faster and mixes more thoroughly. So if you're serious about baking, the stand mixer is key. (Costco has them cheaper than other places ~$240)
  18. Offset spatula
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    This isn't a MUST have item but it will make your life easier and it cost $5. Use it to spread cake or brownie batter evenly in a pan. Use it to frost baked goods easily. Totally worth the minimal price. Get a 4 1/2-inch one. It's the most versatile size.
  19. Flexible bench scraper
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    Again, nice to have but not a must. Great for scraping out dough in a bowl or cleaning up your work surface. I have a bunch of them that I got for free at events. I don't know how much they cost but they can't be too much if people keep on giving me free ones.
  20. The right ingredients
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    I get it. You don't want to buy both bittersweet AND unsweetened chocolate for the recipe. And you know what? It'll probably come out OK with just bittersweet. But it'll also come out better if you use both. The ingredients listed in a recipe are there for a reason. If that recipe had listed 2 different chocolates, it's because the developer probably tried it with just 1 chocolate and thought it was better with 2. Don't waste calories on OK baked goods. Go the extra mile and make it great.
  21. Quality ingredients
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    Much like the right ingredients, buying quality ingredients makes a difference. Cheap imitation vanilla will make your buttercream frosting taste one dimensional and chemically. Generic butter isn't as good as European style butter. Grocery store brand chocolate chips aren't going to taste as good as a high quality chocolate bar you chopped yourself. Little things make the difference in the end product. You don't have to spend major bucks for the best. But buy "better" and you'll notice it.
  22. Patience & a willingness to fail. Because the more you fail, the more you learn and get better at it. And that leads to awesome desserts...
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    Here's the thing about baking. Everyone's kitchen is different. And unlike cooking, where you can adjust seasonings on the fly or lower/raise the heat automatically, baking requires a leap of faith. You follow the instructions and place the batter or dough in the oven and then hope it comes out right. Sometimes it will fail. But hopefully you will learn something from that fail and improve the next time. The more you do it, the better you get. And even the fails are usually pretty good...