The BEST yellow cake recipe I've ever had, probably because there is one unusual ingredient: brown sugar. It makes the cake less traditional but a lot more MOIST. (Hallelujah!) I'm in love with this brown sugar cake and the ridiculous amount of chocolate frosting that goes with it.
Preheat oven to 325 degrees F. Grease 2 9-inch cake pans with butter or nonstick spray, then coat with a small amount of flour, tapping out the excess over your sink. Then trace the bottom of the cake pans onto parchment paper, cut out the circles, and put them in the bottom of the pan.
In a medium saucepan, melt 1 cup butter over medium heat. Stir in the water and whisk until combined. Bring to a boil over medium heat and boil for about 30 seconds. Remove pot from heat and let sit aside to cool.
Meanwhile, in a large bowl, whisk together the white sugar, flour, and 3/4 teaspoon kosher salt.
In another medium bowl, whisk together 2 eggs. Slowly sprinkle baking soda and baking powder over the top while you whisk. Beat until there are no lumps. The mixture may foam, and that's ok!
Stir in 1 tablespoon of vanilla bean paste and 1 cup brown sugar.
When the butter mixture in the pot has cooled enough to handle, stir it into the flour mixture. Then add the egg mixture. Each time mix only until combined.
Lastly, fold in the sour cream. DON'T over mix!!
Divide the batter evenly between the 2 prepared pans (I use a scale to make sure they were even). Drop the cakes on the counter from a few inches above to get out some of the air bubbles.
Bake at 325 for about 34-40 minutes, rotating the pans halfway through. Remove from the oven when a toothpick comes out of the center clean.
Let cakes cool in the pans for 10 minutes, then carefully loosen edges with a knife and invert onto a cooling wrack. Let cakes cool completely.
Wrap the cakes securely in plastic wrap and freeze for about an hour or 2. (This is only so that it's easy to frost the cake. If you are in a hurry and presentation isn't an issue, frost as soon as they are cool!)
For frosting and assembly:
In a large bowl or stand mixer, use the whisk attachment to cream the butter for 2 minutes, scraping the sides and bottom of the bowl. Add the cocoa and 4 cups of powdered sugar in increments, adding the cream in between. Beat well after each addition, scraping the sides of the bowl often.
Add 3/4 teaspoon kosher salt and 2 teaspoons vanilla bean paste. Beat well.
Add the 5th cup of powdered sugar if you like. Frosting consistency is kind of a personal preference, and sometimes it depends on my mood!
Smear a bit of frosting on the bottom of a cake plate. Place 1 cake on top, then cover the top with about 1 cup of frosting (I like to use an offset spatula).
Place the other cake on top, then frost the outside and edges. If you don't want your cake plate to get frosting all over it, line the bottom cake with strips of parchment paper that you can pull out when the cake is completely frosted.
*You can use regular vanilla extract in place of the vanilla bean paste. It will still taste great!