To adjust for high altitude I added an extra ¼ cup water and ¼ cup milk and baked at 315˚. Also to make 2 - 6" rounds and 2 - 8" rounds I doubled the recipe.
Ingredients
3 cups sifted cake flour
1 tablespoon baking powder
½ teaspoon salt
¾ cup butter, room temperature
1 tablespoon plus ¼ teaspoon vanilla extract
2 vanilla beans
1 cup granulated sugar
½ cup water
½ cup milk
6 egg whites
¾ cup granulated sugar FOR THE VANILLA BEAN SWISS MERENGUE
2½ cups sugar
10 large egg whites
4 cups (8 sticks or 2 pounds) unsalted butter, cut into pieces
2 teaspoons pure vanilla extract
Preparation Instructions
Preheat your oven to 350˚ and prepare your cake pans by smearing with butter and cutting out a piece of parchment to fit in the bottom of the pan, place the parchment in the pan and set aside.
In a medium mixing bowl combine the flour, baking powder and salt, set aside.
In the bowl of an electric mixer fitted with the paddle attachment, cream together the butter and vanilla extract and gradually add the sugar, cream until fluffy about 3 minutes.
Take the vanilla beans and slice in half lengthwise and use the back, flat side of a knife to scrape the seeds out and add them to the bowl, save the pods as you will use them in the buttercream.
Combine the water and the milk and alternately add the dry ingredients in fourths and the milk and water mixture in thirds, beating only until smooth between each addition, do not over beat.
In a clean bowl, beat the egg whites until frothy and add gradually (beating well after each addition) the ¾ cup of sugar.
Beat until rounded peaks form, then spread over the cake batter and gently but thoroughly fold the egg whites into the batter
Bake for about 35 minutes, or until a toothpick inserted in the center comes out clean.
Remove from oven and cool in the pans about 20 minutes, then carefully run a knife around the edges and place a cooling rack upside down on top of the cake, holding the cake pan snug against the cooling rack, flip both over so the cake comes out of the pan and gently onto the rack.
Cool completely before icing. TO MAKE THE BUTTERCREAM
Place the egg whites, leftover vanilla bean pods and sugar in a heat proof bowl (I use my kitchenaid bowl) and place over a pot of boiling water. Whisk briskly until sugar has melted, you can test it by rubbing a little of the mixture between your fingers, it should feel smooth. Remove from heat and remove the vanilla bean pods and discard.
Place the bowl on your mixer and fit with the whisk attachment. Beat on high speed until the whites have cooled to room temperature, about 10 minutes.
Once the mixture has cooled start adding the butter a piece at a time. It may start to look curdled at some point at this stage but have no fear, it will smooth out again, just keep beating.
Switch to the paddle attachment and add the vanilla extract.
Have fun icing your cake!
Recipe by Foods of Our Lives at https://www.foodsofourlives.com/2013/06/vintage-vanilla-bean-brides-cake/