Preheat oven to 350 degrees F.
In the bowl of a stand mixer, beat the butter, sugar, salt, and vanilla paste until creamed. Add room temperature yolks and combine well. Combine the baking flour and all-purpose flour. Beat in half the flour and half the milk then add remaining milk and flour and combine well. Then transfer batter to parchment lined sheet pan or 13-inch round cake pan. Bake about 45 minutes to 1 hour, or until a toothpick inserted in the center of the cake comes out clean. Assemble cake using the Swiss Buttercream.
Whisk whites and sugar over a double boiler until 140 degrees F. Transfer egg mixture to mixer with whisk and whip on high until room temperature. Add vanilla and butter then whip until fluffy.
Recipe courtesy of Courtney Clark