Chocolate Banana Brownies with a Peanut Butter Swirl

INGREDIENTS

box brownie mix (I use Ghirardelli)

1 cup

mashed overripe bananas (about 2)

large egg

2 tbsp

vegetable/canola oil

for the peanut butter swirl:

1/2 cup

creamy peanut butter

4 tbsp

unsalted butter, softened

1/3 cup

powdered sugar

1 tsp

vanilla extract

salt