Preheat the oven to 325°F. Line a 9×13-inch pan with foil or parchment paper. Spray with nonstick spray.
Melt the chocolate in a glass bowl in your microwave in small bursts of 30 seconds; stir after each burst and remove from microwave when melted and smooth. Set aside to cool slightly. (If you don't have a microwave, melt the chocolate in the top of a double boiler-- or set a glass bowl on top of a pan of simmering water).
In a large mixing bowl, use an electric mixer to combine the butter, peanut butter and brown sugar. Beat in the eggs and chocolate extract. Mix in the melted chocolate. Mix in the flour. Stir in the peanut butter chips.
Scrape the batter into the prepared pan. Sprinkle peanut butter cup candy pieces on top, pressing pieces lightly into the batter.
Bake 25 to 35 minutes. Watch closely and remove from oven when toothpick inserted into center comes out clean. Let cool completely.
Refrigerate until the brownies are well chilled- if overnight, cover with plastic wrap. When ready to cut, remove from the refrigerator and turn onto a cutting board. Carefully peel off the foil and use another cutting board to flip the brownies back upright. Use a large, sharp knife to cut into squares.