Preheat the oven to 350°F (175°C).
Spray two 8-inch (20cm) round cake pans with cooking spray. Line the pans with a parchment paper and spray the parchment paper lightly with cooking spray. (Note 4)
In a medium bowl, whisk flour, baking powder, baking soda and salt.
2 cups all-purpose flour, 2 ½ teaspoons baking powder, ¼ teaspoon baking soda, ½ teaspoon coarse kosher salt
In a mixing bowl with paddle attachment, or using a handheld electric mixer, beat butter and sugar on medium high speed until fluffy, 3-5 minutes. Scrape the sides of the bowl halfway.
2 sticks unsalted butter, 1 cup granulated sugar
Add eggs, vanilla, and butter extracts and mix on medium high speed until well incorporated, 1 minute.
2 large eggs, 2 egg yolks, 2 teaspoon pure vanilla extract, 2 teaspoons butter extract
Add half of the flour mixture and mix on low speed until just combined.
Add buttermilk and mix on low speed. Then add the remaining flour mixture and mix until just combined, about 30 seconds. Don’t overmix!
1 cup buttermilk
Divide the batter evenly into the prepared pans and smooth the tops. Bake the cake for 27-30 minutes, or until the cakes are golden and inserted toothpick comes out clean.
Let the cakes rest in the pans for 3 minutes. If needed, loosen the edges with a knife and invert the cakes onto a wire rack to cool completely. (At this point, cake layers can be wrapped and stored at room temperature for up to 1 day, or frozen for up to 1 month.)