Preheat oven to 350°F (either convection or regular)

All ingredients should be at room temperature. Sift the cake flour, baking powder, baking soda, and salt. In another bowl whisk together the sour cream and milk. Set aside.

Spray baking dish and set aside.

In the bowl of a stand mixer fitted with the paddle attachment (or with a hand mixer) cream butter and sugar until light and fluffy. Add the eggs one at a time, beating well after each addition. Add the extracts with the last egg.

Alternately add milk and dry ingredients, beginning and ending with dry.

Pour batter into prepared pan. Bake immediately. Bake in preheated oven until a cake tester or toothpick comes out with a few clinging crumbs, approximately 20-25 minutes. Be careful not to over bake or it will dry out.

Allow the cake to cool 10 minutes in the pan then turn out onto a wire rack. Remove the parchment from the bottom of the cake and allow to cool completely.

In the bowl of a stand mixer fitted with the paddle attachment beat the butter until smooth and lightened slightly on medium-high speed.

Reduce the mixer speed to low and add the powdered sugar ½ cup at a time, allowing it to mix in completely before adding the next batch.

Once all the sugar has been incorporated add the vanilla and vanilla bean seeds (optional) and mix on medium speed until light and smooth.

Switch to the whisk attachment and add cream while mixing on medium-low speed. Then increase the speed to high and whisk until light and fluffy and white.

TIP To remove the bubbles, switch back to the paddle and mix on low speed for 2-3 minutes. This will make the buttercream more dense and it will not frost as many cupcakes or cover as much cake but it will give a smoother finish to a frosted cake.

Place the first layer on a cake plate or cake stand or cake board set on a turntable. You can “glue” the board to the turntable and the cake with just a dab of frosting.

Place about 1 cup frosting on the top of the layer and spread smooth.

Set the second layer on top. I like to stack it upside down so that the bottom of the cake layer becomes the top of the cake. This gives you a perfectly flat top without having to level the cake. In everyday life that is wasteful unless you are going to make vanilla cake pops.

Place another 1 cup on top and spread smooth. Spread a thin layer of buttercream around the edges, pressing it into any gaps between layers. Smooth out. This is a crumb coat, so don’t stress too much. Chill the cake 30 minutes. If you are adding a filling, you should chill after adding the second layer before crumb coating to set the dam and lock in the filling.

Spread the remaining buttercream on top and smooth it out towards to edges, allowing it to fall over the sides Smooth it over the sides. Either make decorative swirls or use a bench scraper to make smooth sides and a large offset spatula to smooth out the top.

I used a closed star tip (Ateco 845) to pipe the rosettes.