1 cup peanut butter cups (about 7-8 cups), chopped
Preheat oven to 350°F.
Line an 8 1/2 x 4 1/2 loaf pan with parchment paper, leaving enough paper on the sides to lift out the baked loaf when it is finished.
In the bowl of a stand mixer, cream softened butter and brown sugar on medium speed until light and fluffy, about 5 minutes. Add sour cream and mix well, scraping down the sides of the bowl as needed. Add eggs one at a time, mixing well between additions. Add vanilla and mix well, scraping down the sides to ensure the mix is uniform.
Whisk flour, baking soda and salt together in a medium bowl. With the speed off, add flour mix to the mixer and beat on low until just combined. Add mashed bananas and mix on low until just incorporated. Add chopped peanut butter cups and mix gently with a spatula until incorporated.
Pour into prepared loaf pan, and use a spatula to smooth the top. Bake for about 60 minutes, until a knife inserted into the center of the cake comes out clean. Let cake cool completely before slicing.