Ingredients at a glance

Step 1 - Whisk oil, melted butter and sugar

Step 2 - Whisk in egg and vanilla

Step 3 - Whisk in milk and yogurt

Step 4 - Add in flour and baking powder

Step 5 - Divide the mixture and add cocoa powder to one

Step 6 - Fill the muffin pan with both mixtures

Step 7 - Bake in a pre-heated oven at 350 F for 18 minutes

Full recipe with marble swirl buttercream here.