Make the Cupcakes:

1. Preheat oven to 350°F. Line a muffin tin with 12 cupcake liners.
2. In a medium-sized mixing bowl, whisk together the flour, baking soda, and salt; set aside.
3. In a stand mixer fitted with the paddle attachment, beat the butter, peanut butter, and both sugars together until light and fluffy, about 2 minutes. Add in the egg, egg yolk, and vanilla, mixing until combined. Add the Greek yogurt and milk, and continue beating until fully incorporated. Add the dry ingredients, and mix until just combined.
4. Evenly distribute batter among cupcake liners, then bake for 20-23* minutes, or until you gently press on the top and it springs back instantly instead of leaving a dent. Allow cupcakes to cool for 15 minutes before transferring to a wire rack to cool completely.

Make the Frosting:

1. Click the link above for the recipe.