Preheat oven to 350 degrees. Line a 12-cup muffin pan with baking liners.
In a large mixing bowl, add cake mix, water, eggs, and oil. Using a hand or stand mixer, mix on low speed for 1 minute and then on medium for 1 minute.
Add in peanut butter and mix
Fold in chocolate chips and ½ cup of chopped mini Reese’s cups.
Fill each muffin cup 2/3 of the way with batter. Sprinkle with remaining ¼ cup chopped mini Reese’s cups and bake 18-20 minutes or until it springs back when touched. Let cool.
In a large mixing bowl or stand mixer, beat butter for 2 minutes, until light and creamy.
Add in the vanilla, and sea salt and beat for 30 seconds. Mix in the peanut butter and chocolate hazelnut spread until well incorporated.
Slowly alternate between the powdered sugar and creamer until light and fluffy. If mixture is too thick, add more creamer, 1 tablespoon at a time.
Place in piping bag and frost cupcakes. Sprinkle with the remaining chopped mini Reese’s cups.