In the bowl of an electric mixer fitted with a paddle, beat the butter and peanut butter on medium speed until well blended.
1/4 cup unsalted butter, 1/2 cup creamy peanut butter
Slowly add the milk, then gradually add the powdered sugar until frosting reaches the desired consistency. I use about 1 1/4 cups to get a relatively stiff frosting, but the amount may vary slightly depending on the brand of peanut butter used.
1/4 cup milk, 1 1/4 cups powdered sugar
Pipe or spread about 1/2 to 1 teaspoon of frosting onto the flat side of a Nilla Wafer.
50 Nilla Wafers
Sprinkle on a pinch of mini chocolate chips.
1/2 cup mini chocolate chips
Top with a second Nilla Wafer.
Gently squeeze the wafers together, then add more mini chocolate chips to the edges, if desired.
Repeat with remaining cookies and frosting.