Pulse the bread into fine crumbs using a food processor.
Note: if you forget to leave the bread out overnight, you can dry it out in a 300 degree oven for 10-15 minutes.
In a large bowl, mix together the bread crumbs, butter, and brown sugar. Press into a 9-inch round pie plate. Refrigerate at least 30 minutes before filling.
In a large mixing bowl, beat together the cream cheese, peanut butter, powdered sugar, and milk until smooth and creamy, about 2-3 minutes.
In another large mixing bowl, beat the heavy cream until it thickens and forms stiff peaks, about 3-5 minutes.
Fold the whipped cream into the peanut butter mixture until fully incorporated, then fold in 1 cup peanut butter cups. Spread onto the chilled crust and top with the remaining peanut butter cups.
Refrigerate or freeze until fully chilled, at least 4 hours or overnight. Serve.