CAKE

1. Preheat oven to 350 degrees.  Line two 9-inch round cake pans with a round of waxed or parchment paper. Grease and lightly flour the pans, tapping out the excess flour. Set aside.
2. In a medium bowl, whisk or sift together the flour, baking powder, baking soda & salt. Set aside.
3. Add the butter to the large bowl of a stand mixer fitted with the paddle attachment, or use a hand mixer. Beat the butter on high speed for about 1 minute, until it looks light and creamy. Add the sugar on medium speed and beat for about 5 minutes, until the mixture is very light and fluffy, scraping down the sides and bottom of the bowl as needed. 
4. Add the eggs, one at a time, beating on medium speed after each addition until each one is fully incorporated. Mix in the vanilla.
5. With the mixer on low, add the flour mixture in three additions, alternating with the buttermilk, beginning and ending with the flour, (1/3 flour, 1/2 buttermilk, 1/3 flour, 1/2 buttermilk, and 1/3 flour). Mix just to incorporate the flour. Do not over mix.
6. Divide the batter evenly between the two cake pans, spreading the batter out evenly with an offset spatula.  
7. Bake the cakes on the middle oven rack for 25-38 minutes, or until a toothpick test comes out with just slightly moist crumbs on it. The tops should be golden brown. Leave the cakes in the pans for about 10 minutes, then run a knife around the edges to loosen cakes. Invert the cake layers onto wire racks to cool.

VANILLA BUTTERCREAM FROSTING

1. Add the butter to the mixing bowl of a stand mixer, fitted with the whisk attachment. Beat the butter on high for about 3 minutes, until it’s very light colored and creamy. Stop and scrape down the sides of the bowl as needed. 
2. Sift 4 1/2 cups of powdered sugar into a large bowl. Turn the mixer to low. Re-measure the powdered sugar and slowly add it to the mixing bowl, one cup at a time. Stop after two cups, and add 1 tablespoon of your milk, so that it doesn’t become too thick at one time. 
3. Once the sugar is incorporated enough so that it doesn’t splatter out of the bowl, turn the mixer to medium speed and add the salt, vanilla, and and remaining milk. Mix on medium high speed for about 1 minute, until all ingredients are well combined. If the frosting seems too thick, add a tiny bit more milk, one teaspoon at a time, until you have the perfect spreading or piping consistency.  
4. TO FROST: Place one cake layer on a cake plate or stand. Spread about 1 1/2 cups of the frosting over the layer, stopping about 1/4 inch from the edges of the cake layer. Place the top layer over the frosting. Spread the remaining frosting over the sides and top.
5. Place cake in an airtight cake container and leave at room temperature. 
6. Cake will stay fresh for up to 3 days. If you want to refrigerate the cake leave it covered and set it out of the refrigerator about 30 minutes before serving it.