Preheat oven to 350 degrees and line a muffin pan with liners or baking spray.
In a bowl, combine the butter, peanut butter, sugar, and vanilla.
Beat together until smooth and creamy.
Add in the eggs and sour cream. Stir to combine.
Add in the cocoa powder, baking powder, and salt.
Once combined, add in the flour and milk mixing until smooth.
Fold in the chocolate chips.
Spoon batter into prepared muffin tins about 3/4 full.
Bake in preheated oven for about 25 minutes, or until toothpick comes out clean when inserted in middle.
Remove from oven and place on cooling rack for a few minutes prior to enjoying!