• Preheat oven to 350 degrees F. Line 2 regular muffin tins with cupcake liners. 
• Mix together the cake mix, milk, eggs, oil and Greek yogurt until smooth. Spoon batter into cupcake pans, filling the liners 1/2 full. 
• Place a Reese's PB cup into the center of the batter in each cup (it's okay if the the tops of the Reese's are showing, like photo above). 
• Bake cupcakes for 16-20 minutes or until done. Allow to cool completely before frosting.

For the Peanut Butter Frosting

• Beat together butter, and peanut butter and mix until smooth. 
• Add powdered sugar and vanilla and beat again until combined. 
• Add milk and mix until light and fluffy. (Add more milk or powdered sugar if needed to make the frosting thicker or thinner). 
• Frost cupcakes (I used a wilton 1M tip in the photos above). 
• Chop up the remaining pieces of Reese's and gently press into frosting. 
• Store leftover cupcakes, covered, in the fridge for 3-4 days.