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.