Preheat oven to 350° F. Line a 8-inch or 9-inch square baking pan with parchment paper or grease with nonstick spray.
In the bowl of a stand mixer fitted with a paddle attachment, beat together the butter, peanut butter, and brown sugar on medium high speed until light and creamy, 3-5 minutes. Scrape down the bowl as necessary. Mix in the eggs one at a time, mixing after each, followed buy the vanilla extract.
In a separate bowl combine the whole wheat flour, baking soda, and salt. Add to the stand mixer and mix on medium low speed until combined. Add the chocolate chips and mini peanut butter cups and mix on low until just combined.
Press into the prepared baking pan and bake until edges are golden, about 35-40 minutes. Let cool completely before slicing.
Note: If desired, you can omit the mini peanut butter cups and increase semi-sweet chocolate chips to 2 cups (400 grams).
Calories: 416kcal, Carbohydrates: 48g, Protein: 9g, Fat: 23g, Saturated Fat: 10g, Cholesterol: 37mg, Sodium: 275mg, Potassium: 301mg, Fiber: 4g, Sugar: 30g, Vitamin A: 223IU, Vitamin C: 1mg, Calcium: 51mg, Iron: 2mg