Line three 8-inch (21cm) round cake pans with parchment paper and spray the pans with cooking spray as well.
Preheat the oven to 350°F (175°C).
In a small bowl, whisk together flour, baking powder, baking soda and salt. Set aside.
3 cups all-purpose flour, 2 ½ teaspoons baking powder, 1 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 until fluffy, 3-5 minutes. Scrape the sides of the bowl halfway.
2 sticks unsalted butter, 1 ½ cups granulated sugar
Add the eggs and vanilla bean paste. Mix on medium high speed until fluffy and smooth, scraping the sides of the bowl halfway, 2-3 minutes.
4 large eggs, ½ tablespoon vanilla bean paste
Add half of the flour mixture and mix on low speed until just combined.
Add the 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, at room temperature
Divide the batter evenly into the prepared pans and smooth the tops. Bake the cake for 25-27 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.)