This is becoming my go-to way of dressing up plain brownies. Adapted from this recipe, I just add the peanut butter filling to a 9 x 13 batch of brownies. A couple notes: 1) Making the PB filling as written gives you brownies that are at least half PB. If you don't want that much, use scant measurements or half it. 2) These seem to keep better than regular brownies, no doubt due to all the extra fat. They'd probably mail well.
Peanut butter mixture:
- ½ cup (8 tablespoons) unsalted butter, melted
- 1 cup powdered sugar
- 1½ cups creamy peanut butter
- ½ teaspoon salt
- 1 teaspoon vanilla extract
- Mix brownies as directed, pour into prepared pan.
- Mix all peanut butter filling ingredients, then spoon it out on top of brownie batter.
- Using a knife or spoon (or finger if you want, I guess), swirl them together.
- Bake as directed on brownie mix.