Preheat oven to 350 degrees.
Line cupcake tins with paper liners.
Using an electric mixer, cream the butter and peanut butter together, then add cream and the brown sugar.
Add the beaten egg and vanilla into the creamed mixture and beat until well incorporated.
Whisk together the flour, baking powder, and salt in a bowl.
Gradually add the dry ingredients to the creamed mixture.
Alternate the addition of the dry ingredients with the milk, a third of each at a time.
With a medium ice cream scoop fill the lined muffin cups two-thirds full.
Bake the cupcakes at 350 degrees for 20-25 minutes or until a toothpick comes out clean.
Allow the cupcakes to cool in the pan for 10 minutes.
Transfer the cupcakes to a wire rack to cool completely for about an hour.