Follow the steps in order for the best result.
In a large bowl, combine the peanut butter, 1/2 cup of margarine (or butter), and powdered sugar. Using a pastry blender, cut the ingredients together by hand until well combined. Avoid using an electric mixer, as this can make the mixture too creamy and affect the final texture; the mixture may need to be kneaded slightly.
Line a 13x9x2 inch baking pan with aluminum foil. Lightly butter your hands and evenly spread the peanut butter mixture into the prepared pan, pressing firmly to create a smooth layer.
Prepare a double boiler by bringing water to a boil in the lower pot. In the top pot, combine the chocolate chips and 1 tablespoon of melted margarine (or butter). Ensure that no water gets into the chocolate mixture.
Stir the chocolate mixture constantly until the chocolate chips are completely melted and the mixture is smooth and glossy.
Immediately pour the melted chocolate evenly over the peanut butter layer in the pan.
Allow the peanut butter cups to cool and harden slightly at room temperature.
Once partially set, cut the candy into squares. A pizza cutter works exceptionally well for achieving clean, even cuts!
After cutting and allowing the chocolate to fully set, store the peanut butter cups in a covered container, such as a Tupperware container, to maintain their freshness.