Chocolate Banana Rye Muffins

Name: Chocolate Banana Rye Muffins
Ingredients: 1 cup (125g) all-purpose flour; 1/2 cup (65g) rye flour; 1/2 cup (35g) Dutch-process cocoa powder; 1 teaspoon baking powder; 1/2 teaspoon baking soda; 1/2 teaspoon kosher salt; 2 very ripe bananas, mashed (about 2/3 cup mashed); 1 large egg, at room temperature; 3/4 cup (150g) packed light brown sugar; 2 teaspoons vanilla extract; 1/3 cup buttermik; 6 tablespoons (80g) unsalted butter, melted and cooled to lukewarm; 1 cup dark chocolate chips or chunks; cacao nibs, for topping; raw or turbinado sugar, for topping