Line an 8 or 9 inch square pan with parchment paper, nonstick foil or regular foil. If using regular foil, rub the foil generously with some softened butter.

Melt about ¾ of the chocolate in a metal bowl set over but not touching simmering water or in a double boiler. Remove from heat and stir in the remaining chopped chocolate. Stir well until chocolate is completely melted.

Stir the peanut butter into the melted chocolate.

Scrape the melted chocolate mixture into a mixing bowl and stir in the cereal, followed by the marshmallows, peanuts and Reese's (if using).

Pour into the pan and press down so that it’s tight. Chill for a few hours or until very firm, then lift from the pan and cut into squares.