Preheat the oven to 350˚F (177˚C). Place 2 muffin pans with 14 paper liners.
In a large mixing bowl, sift together the flour, brown sugar, cocoa powder, baking soda, and salt.
In a small bowl, whisk together the milk, egg, melted butter and vanilla extract. Add to the flour mixture. Whisk until just combined.
Add the blueberries and ¼ cup chocolate chips. Fold into the batter gently. Divide the batter into the prepared muffin pans. Top each muffin with 5 – 6 chocolate chips.
Bake in the oven for 18 – 22 minutes. Test the muffins with a toothpick for doneness. The toothpick should come out clean. Remove the pans from oven and cool for 5 minutes. Carefully remove the muffins to a wire rack to cool. Serve warm or at room temperature.