IMPORTANT: Make sure all your ingredients are at room temp and you're using a scale to measure. Substituting ingredients may cause the recipe to fail. (see notes at the bottom of the recipe)
Heat oven to 335º F - Prepare three 6"x2" cake pans (or two 8"x6" cake pans) with cake goop or another preferred pan release -
Measure out 4 ounces of your buttermilk into a separate container. Add in your vegetable oil and set aside. (if doubling our tripling your recipe, remember to adjust this amount as well)
Combine the remaining buttermilk with your vanilla and eggs. Whisk lightly and set aside.
Measure out the flour, sugar, brown sugar, baking soda, baking powder, and salt and place them into the stand mixer bowl with the paddle attachment.
Turn the mixer on the slowest speed (setting 1 on Kitchen Aid mixers). Add in your browned butter to the flour mixture. Let mix until batter resembles coarse sand.
Add your buttermilk and oil to the flour mixture.
Increase mixing speed to medium (setting 4 on Kitchen Aid mixer) and mix for 2 full minutes. Let the mixture whip up until it has thickened and lightened in color. It should look like soft-serve ice cream. If you do not let the batter mix fully, you will end up with very short, crumbly cakes that do not rise.
Scrape the bowl. This is an important step. If you skip it, you will have hard lumps of flour and unmixed ingredients in your batter. If you do it later, they will not mix in fully.
Add your egg mixture in three parts, letting the eggs incorporate for 5-10 seconds between additions. Scrape the bowl halfway through.
If your batter is curdled and broken at this point, your milk/eggs where too cold and your cake may not rise.
Divide your cake batter between your pans. I weigh my pans to make sure there is the same amount of batter in each pan.
Bake for a minimum of 30 minutes before you check for doneness. Remember, bigger pans take longer to bake than smaller pans. I use a baking core for pans over 12". Cakes are done when a toothpick comes out clean or the tops spring back when you lightly touch them.
After cakes have cooled for 10 minutes or the pans are cool enough to touch, flip the cakes over onto cooling racks to cool completely. Wrap in plastic wrap and chill in the refrigerator or freeze for one hour to speed up cooling.
Frost and decorate as desired