Instructions

For cake:

Position a rack in the upper third of the oven and preheat oven to 350 degrees F. Line three 6-inch or two 8-inch cake pans with parchment paper and set aside.
In a medium bowl, whisk together flour, baking powder and salt. Set aside.
In a small bowl, whisk together milk, vanilla extract and vanilla bean seeds. Set aside.
In a stand mixer, fit with a paddle attachment, cream the butter and sugar until light and fluffy. This may take 3 to 5 minutes. Scrape down the sides of the bowl to make sure everything is well incorporated.
Add the eggs, one at a time, beating for one minute after each addition. If the batter begins to looks a bit curdled, that’s alright. With the mixer on low speed, alternately add the flour mixture and the vanilla milk mixture in three batches, starting and ending with the flour. When the batter is almost combined, stop the mixer and finish mixing the batter with a spatula, making sure that any flour bits at the bottom of the bowl are well incorporated.
Divide into the lined cake pans and bake for 25 minutes or until golden and a cake tester inserted in the center comes out clean. Allow to cool in the pan for 10 minutes before removing to cool completely before assembly.

For the Champagne soak:

Combine the sugar and water in a small sauce pan set over medium heat. Bring to a boil, stirring often to dissolve the sugar. Remove from heat, and add the champagne and stir. Set aside to let cool.

For the frosting:

With an electric mixer, beat together sugar and butter. Mix on low until well blended, and then on medium for another two minutes. Add vanilla and champagne, beating on medium for another minute.

Assembly
To assemble, wait for cakes and soak to be completely cool. Then, start layering cake, brushing or drizzling with champagne soak. Spread with a thin layer of frosting and then a hearty layer of jelly. Continue until top layer, then cover with frosting, and decorate as desired.