Preheat oven to 350 degrees. Butter two 8-inch pans and line with parchment; butter the parchment and dust the pans with flour, tapping out the excess.
Whisk together flour, baking soda, baking powder, and salt in a large bowl.
Cream the butter and sugar in the bowl of a standing mixer fitted with a paddle attachment on medium high speed until light and fluffy, 3 to 5 minutes. Add eggs one at a time, mixing thoroughly between each addition. Beat in sour cream and vanilla.
Reduce mixer to low. Add flour mixture in three additions, alternating with the Champagne, beginning and ending with the flour.
Transfer batter to prepared pans and bake until golden brown and a cake tester comes out clean, about 45 minutes. Let cakes cool in the pan 15 minutes, then transfer to a wire rack to cool completely.
No need to spring for the French stuff. Your caterer can pop prosecco, cava, or riesling into this batter instead, as long as the variety classifies as sparkling wine.