2 1/2 cups all-purpose flour
1 Tbsp baking powder
1/2 tsp fine salt
1 cup unsalted butter, softened
1 1/2 cups granulated sugar
4 large eggs, room temperature
4 tsp pure vanilla extract
1 cup buttermilk, or plain kefir, room temperature
Preheat oven to 350˚F. Butter and flour two 9″ cake pans, tapping out excess flour.
In a medium bowl, whisk together flour, baking powder and salt. Set flour mixture aside.
In a large mixing bowl using an electric hand mixer (or stand mixer), beat butter and sugar on medium-high speed for 5 minutes until thick and fluffy, scraping down the bowl as needed.
Add 4 eggs, one at a time, beating well with each addition then scrape down the bowl. Add 4 tsp vanilla extract and beat to combine.
Reduce mixer to medium speed and add the flour mixture in thirds alternating with the 1 cup of room temperature buttermilk, allowing the flour and buttermilk to incorporate with each addition. Scrape down the bowl as needed and beat until just combined and smooth.
Divide batter evenly between 2 prepared cake pans and spread out the batter into the pans smoothing out the tops with a spatula. Bake on the center rack at 350˚F for 28-30 minutes. Rest in pans for 10 minutes then run a knife or thin spatula around the edges to loosen and turn out onto a wire rack to cool completely before applying