1. Beat the butter or margarine in a mixer using the whisk attachment until creamy, about two minutes. Add both sugars and beat for an additional two minutes. Mix in the peanut butter and egg. Add flour, baking soda, baking powder, and salt and mix just until well combined and a smooth dough forms.
2. Wrap the dough in Gefen Parchment Paper and refrigerate for at least three hours. This helps keep the cookies from flattening too much during baking.
3. When dough has chilled, preheat oven to 375 degrees Fahrenheit (190 degrees Celsius). Line two baking sheets with parchment paper. Shape the cookies by using a large three-tablespoon cookie scoop (about two and 1/4-inch/5.7-centimeter diameter) and place spread apart on parchment paper, eight scoops per baking sheet. Flatten each ball in a crisscross pattern, using a fork. (It helps to dip the fork in sugar to keep it from sticking to the dough.)
4. Bake cookies until light brown, about 11–12 minutes. Remove the cookies from the oven and let cool on their baking sheets for two minutes. Gently transfer to a wire rack to cool completely.
5. Once cookies have cooled, break up the chocolate bars and place squares into the top of a double boiler. Add water to the bottom of the boiler and bring to a rolling boil. Add butter or oil and melt chocolate until smooth and no lumps remain, stirring gently.
6. While water is boiling, spread the chocolate onto the top of a cookie, using a small rubber spatula or the back of a spoon. Before chocolate sets, quickly sprinkle the cookie with chopped peanuts. Repeat for remaining cookies. Place on baking sheets and refrigerate for 10–15 minutes or until completely set.