1. Line a mini muffin tin with 20 foil muffin papers. Combine filling ingredients in a medium-sized bowl. Refrigerate for a few minutes.
2. Melt chocolate until smooth. Add two teaspoons peanut butter and stir to combine.
3. Working with one muffin cup at a time, drop melted chocolate from a spoon to generously coat bottom of cup. Spoon approximately half a teaspoon of filling into the center of the cup, trying to avoid touching sides of cup. Pour melted chocolate over filling to cover. Repeat with remaining cups. Refrigerate to set.
4. To make the brownies, use your own favorite brownie recipe or the recipe above. If using above recipe, preheat oven to 350 degrees.
5. In a large mixing bowl, combine all ingredients and beat until smooth. Pour into an 11- x 14-inch (25- x 35-centimeter) parchment- paper-lined baking pan. Bake for 45 minutes and remove from oven.
6. When brownies are finished baking, remove from oven and allow to cool five minutes. While brownies are cooling, peel foil papers off peanut butter cups.
7. Press cups into brownies in even intervals, pushing in deeply, until the surface of each cup is aligned with the surface of the cake. Cool to room temperature.