How to Make It
Preheat oven to 350°F. Peel and chop 2 Anjou pears (about 2 cups); set aside.
Beat unsalted butter; granulated sugar; and light brown sugar with an electric mixer on medium speed until light and fluffy, about 4 minutes. Add 2 large eggs, 1 at a time, beating on low just until combined after each addition. Add vanilla extract; beat just until smooth.
Whisk together all-purpose flour, unsweetened cocoa, baking powder, baking soda, and kosher salt in a large bowl. Add to butter mixture in thirds alternately with whole buttermilk, beginning and ending with flour mixture, beating on low just until combined after each addition.
Fold in 1 3⁄4 cups chopped pears and 1 cup semisweet chocolate chunks. Divide batter among 2 (12-cup) muffin pans lined with paper baking cups. Sprinkle tops with 1⁄4 cup semisweet chocolate chunks and remaining 1⁄4 cup chopped pears.
Bake in preheated oven until a wooden pick inserted in center of muffins comes out with moist crumbs, 25 to 30 minutes. Cool in pans on wire racks 15 minutes. Remove muffins to wire racks to cool completely, about 30 minutes.