Preheat the oven to 350 degrees F. Grease the bottom of two 8-inch round cake pans and line with waxed paper or parchment paper.
Sift together the flour, salt and baking powder, then set aside. In a large bowl using an electric mixer, cream the granulated sugar and butter together until light and fluffy. Add the vanilla and eggs and beat until thoroughly mixed. Alternate adding the flour and the milk, a little at a time, beating well after each addition, then continue beating for 1 minute. Spread the batter evenly into the prepared pans. Bake until a toothpick inserted in the center comes out clean, 30 to 35 minutes.
Cool the cakes in the pans on a wire rack for 10 minutes. Remove the cakes from the pans and cool completely on the wire rack.
Frost the top of one cake layer with Swiss Buttercream and place the second cake layer on top. Then frost the top and sides of the cake. Serve at room temperature.
Yield:enough to frost one 8- to 10-inch layer cake
Put the egg whites in the bowl of a stand mixer fitted with the whisk attachment. Start the machine on medium-slow speed and whip until the eggs begin to get frothy. Turn the speed to medium.
Slowly add the sugar to the whipping egg whites, dropping the lemon juice in about halfway through the process.
When all the sugar is in, speed up the mixer and whip until stiff peaks form and the meringue is smooth and super shiny.
Turn the speed to medium-low and begin adding the butter. Add it bit by bit so the meringue doesn't slop over the sides of the bowl. At this point, the meringue will fall and look ruined and broken. It's not. This is what happens and it's okay. If the meringue doesn't fall, add a little butter until it does.
Turn the speed back up to medium-high and walk away. Come back in 10 minutes. Does it look like buttercream? No? Walk away and repeat until it does. If it still doesn't look like buttercream after 30 minutes, add more butter until it does.