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. This is the flour mixture.
In a stand mixer bowl, 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 1/3 of the flour mixture and 1/2 of the milk. Mix again until combined. Repeat the process and mix again. Finish the mixing with the flour. Scrape down the bowl as needed and beat until just combined and smooth. Be careful not to overmix.
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 invert it onto a wire rack to cool completely.
Vanilla Buttercream
Beat butter on a medium speed for 30 seconds until smooth.
Mix in vanilla extract and salt on a low speed.
Slowly add in 7 cups of powdered sugar, 1 cup at a time. Half way through add in 3 Tbsp of heavy cream or milk to make it easier to mix.
Mix on low until the ingredients are fully incorporated and the desired consistency is reached.
If the frosting is too thick, add in 1 tbsp of cream (1 Tbsp at a time). If the frosting is too thin, add 1/4 cup of powdered sugar. Add the desired color.a