1. Preheat your oven to 350°F (175°C) to ensure even baking.
2. Line a muffin tin with paper liners or spray it with baking spray.
3. In a large mixing bowl, whisk together flour, cocoa powder, baking powder, baking soda, and salt.
4. In another bowl, combine sugar, melted butter, eggs, buttermilk, and vanilla extract. Mix well.
5. Gradually add the wet mixture to the dry ingredients, stirring gently until just combined.
6. Gently fold in the chocolate chips or chunks into the batter.
7. Spoon the batter into the prepared muffin tin, filling each cup about ¾ full.
8. Bake for 18-20 minutes, or until a toothpick inserted comes out clean.
9. Let the muffins cool in the pan for 5 minutes before transferring to a cooling rack.
10. For the glaze, whisk together peanut butter and a splash of milk until smooth.
11. Drizzle the glaze over the cooled muffins and allow to set before serving.
