Preheat oven to 350°F. Butter three 8- or 9-inch cake pans. Line the bottom of pans with parchment; butter parchment.

Sift together flour, baking powder, and salt.

In the bowl of a stand mixer fitted with the paddle attachment, cream butter on medium speed until smooth, about 1 minute. With the mixer still running, slowly add sugar and beat until light and fluffy, about 5 minutes. Periodically scrape down sides of bowl.

Reduce mixer speed to medium-low and add the egg yolks one at a time, waiting until one is incorporated completely before adding the next.

Add vanilla extract and beat in. Stop mixer.

Add flour mixture in three equal additions, alternating with buttermilk. After each addition, pulse the mixture to begin incorporating ingredients, then run on low until just incorporated, about 15 seconds.

Transfer batter to a large clean bowl, and clean mixer bowl thoroughly.

Using the whisk attachment on medium, whip egg whites until frothy. Add cream of tartar, if using, and whip on high until stiff, but not dry, peaks form.

Fold egg whites into batter.

Divide batter among the prepared cake pans.

Bake for 30-35 minutes, or until top springs back when press lightly and a skewer inserted into the center comes out clean.

Let cool on a baking rack about 10 minutes. Run a sharp knife around the edge of each cake and remove from pans to cool completely before frosting.