Preheat oven to 350°F (175°C)
Grease and line two 8-inch (20 cm) round cake pans with parchment paper
Gather ingredients: flour, sugar, baking powder, salt, eggs, milk (or buttermilk), neutral oil (or melted butter), vanilla extract, and optional cocoa or flavoring
Whisk dry ingredients in a bowl: flour, sugar, baking powder, and salt
Whisk wet ingredients in a separate bowl: eggs, milk, oil, and vanilla
Pour wet ingredients into dry ingredients and mix until just combined
Add any mix-ins (optional) and fold gently
Divide batter evenly between pans and smooth tops
Bake 25–35 minutes, or until a toothpick in the center comes out clean
Cool in pans for 10–15 minutes
Remove cakes from pans and cool completely on a rack
Level tops if needed (optional)
Make frosting (optional): beat butter, add powdered sugar, add vanilla, and thin with milk/cream to desired consistency
Assemble: place one layer down, spread frosting, add second layer, and frost sides and top
Chill 15–30 minutes for cleaner slices (optional)
Slice and serve