Step 1

Preheat the oven to 350, and spray a 6" round cake pan with 2" sides with cooking spray. Line the bottom of the pan with a round of parchment paper.

Step 2

In a medium-size bowl, beat together the butter and sugar with an electric mixer. Beat very well, about 1-2 minutes.

Step 3

Add the egg and vanilla, and beat until well-combined, about 15 seconds.

Step 4

In a small bowl, whisk together the flour, salt and baking soda. Add half of the this to the batter and beat for just a few seconds before stirring in half of the milk and vinegar. Continue beating. Add the remaining dry ingredients and beat, and then stir in the remaining milk.

Step 5

Scrape the batter into the prepared pan, smooth out the top, and bake on a small sheet pan for 37-39 minutes, until a cake tester comes out clean.

Step 6

Let the cake cool on a wire rack in the pan. Carefully remove it from the pan, pulling away the parchment paper once it has cooled.

Step 7

To make the buttercream, beat the butter in a medium-size bowl with an electric mixer until light and fluffy. Add the powdered sugar, vanilla and heavy cream, and beat until light and fluffy. If the mixture seems too stiff, add a splash more heavy cream.

Step 8

Use a little more than half of the buttercream to frost the cake. If you made the cake ahead of time and frozen it, it's best to apply a crumb coat of buttercream before applying a second layer.

Step 9

Place the remaining 1/4 of the buttercream in a piping bag fitted with a 1M tip, and pipe roses along the outside edge of the cake. To make a rose, pipe a spiral shape, starting inside of moving around the center.