Preheat oven to 350ºF degrees. Spray a 9" x 5" loaf pan with non-stick spray and set aside.
In a large bowl, whisk together flour, baking powder, salt, and mini chocolate chips until combined. Set aside.
In a medium bowl with a handheld mixer or in the bowl of a stand mixer fitted with the paddle attachment, beat peanut butter, granulated sugar, and brown sugar together on medium speed until smooth. Add room temperature eggs one at a time, beating after each addition and scraping down sides and bottom of bowl with a spatula as necessary. After eggs are fully incorporated, use your spatula to scrape down the sides and bottom of the bowl again to ensure everything is well mixed. On low speed, beat in vanilla and buttermilk until everything is combined. Mixture will be runny-- this is ok.
Slowly pour the wet ingredients into dry ingredients and stir gently until there are no more lumps. Be careful not to over mix, as this can cause bread to become tough.
Pour batter into prepared loaf pan and sprinkle with coarse sugar and more mini chocolate chips (both entirely optional). Bake for 56-58 minutes or until toothpick inserted in middle of loaf comes out mostly clean. Bread will continue to bake in pan a bit as it cools. My bread took exactly 57 minutes. Allow bread to cool completely in the pan on a wire rack before cutting. Bread will remain fresh stored in an airtight container or wrapped tightly at room temperature up to 5 days. Loaf may be frozen up to 2 months.
*If you do not have buttermilk on hand, you can make your own: see my post about homemade buttermilk.