Preheat your oven to 350°F (175°C) and line two 9-inch round cake pans with parchment paper.

Cream butter and brown sugar until light and fluffy, about 3-4 minutes.

Whisk eggs together and mix with the creamed mixture, then add melted chocolate and vanilla.

Combine flour, baking powder, baking soda, and salt in another bowl, then alternate mixing with buttermilk.

Fold in sour cream and vegetable oil until just combined.

Divide batter between pans and bake for 30-35 minutes until a toothpick inserted comes out with few moist crumbs.

Let cakes cool in pans for 10 minutes before transferring to a wire rack to cool completely.