Ensure all ingredients are at room temperature and use a scale for precision. Substituting ingredients can lead to recipe failure (see notes below).
Preheat the oven to 335º F and prep three 6"x2" cake pans (or two 8"x6" pans) with cake goop or your preferred pan release.
Measure 4 ounces of buttermilk, add vegetable oil, and set aside. Adjust this amount if you're doubling or tripling the recipe.
Combine the remaining buttermilk with vanilla and eggs, whisk lightly, and set aside.
Place flour, sugar, brown sugar, baking soda, baking powder, and salt in the stand mixer bowl with the paddle attachment.
Start the mixer on the lowest speed (setting 1 for Kitchen Aid mixers) and add browned butter until the batter resembles coarse sand.
Add buttermilk and oil to the flour mixture.
Increase the mixing speed to medium (setting 4 on Kitchen Aid mixer) and mix for 2 minutes until the mixture thickens and lightens in color, resembling soft-serve ice cream.
Ensure thorough mixing; incomplete mixing results in short, crumbly cakes that won't rise.
Scrape the bowl; it's crucial to prevent lumps and unmixed ingredients.
Add the egg mixture in three parts, allowing 5-10 seconds between additions. Scrape the bowl midway.
If your batter curdles or breaks, your milk/eggs were too cold, potentially affecting cake rise.
Divide the cake batter evenly between your pans, preferably by weight for accuracy.
Bake for a minimum of 30 minutes, adjusting for larger pans. A toothpick should come out clean, or the tops should spring back when touched.
Once the cakes cool for 10 minutes or the pans are safe to touch, invert them onto cooling racks to cool completely. Wrap in plastic and chill in the refrigerator, or freeze for an hour to speed up cooling. Frost and decorate to your liking.