• Preheat the oven to 350 F.
• Prepare a 9x13 pan by lightly greasing it.
• In a large mixing bowl, combine the starter, milk, and flour and whisk thoroughly.
• In a separate bowl, beat together the sugar, oil, sour cream, vanilla, salt, baking soda, and cocoa.
• The mixture will be grainy.
• Add the eggs one at a time to this mixture, mixing well after each addition.
• Gently combine the starter mixture into the chocolate mixture, whisking until smooth.
• Pour the batter into the prepared pan.
• Bake for 30-40 minutes, until it springs back when lightly pressed in the center, and a cake tendster in the center of the cake comes out clean.
• Allow the cake to cool on a wire rack completely before frosting.

Chocolate Buttercream Frosting

• In the bowl of a stand mixer fitted with a whisk attachment, beat the butter until soft and fluffy.
• Add in the confectioner’s sugar, cocoa powder, vanilla, and salt and beat until combined.
• Add the milk, 1 tablespoon at a time, until you reach the desired consistency.