Preheat oven to 350°F. Grease a quarter-sheet pan with coconut oil spray and line with parchment paper.

In the bowl of an electric mixer, whisk egg and melted salted butter until smooth and creamy. Add Blondie Bar Baking Mix and chopped peanuts and stir to combine. Spread mixture evenly onto the parchment lined pan.

Bake on center rack of oven 12-15 minutes. Remove and cool completely.

In the bowl of an electric mixer, add 1 stick softened, unsalted butter, peanut butter, vanilla, and salt. Beat on high speed, scraping down the sides of the bowl, until smooth and combined.

Add powdered sugar and heavy cream. Beat on low to combine, then increase to high speed for 5 minutes, scraping the bowl down now and then, until very light and fluffy.

Spread half of the filling on the cooled blondie base. Top with a layer of sliced bananas. Blot bananas with a paper towel to dry. Smooth remaining filling evenly over bananas. Refrigerate until firm (about 1 hour).

Place a small pot with one inch of water over low heat. Place the chocolate, butter, and cream in a heatproof bowl that fits over the small pot. Slowly melt the mixture, stirring occasionally. Remove from heat and allow to cool 5 minutes.

While chocolate cools, chop frozen peanut butter cups into small pieces, or pulse in a food processor.

Smooth melted chocolate evenly over the peanut butter filling and sprinkle with chopped peanut butter cups. Refrigerate 5 minutes, then score just through the chocolate easy slicing. Refrigerate 1 hour or until ready to serve.

Slice into 24 squares, garnish with freshly sliced bananas, and serve.