Preheat the oven to 400°F (200°C). Position an oven rack in the center of the oven. Line a 12-cup muffin tin with paper cups.
Whisk the flour, sugar, cocoa powder, baking powder, and salt in a medium bowl.
Whisk the eggs in a large bowl until lightly beaten.
Whisk in the milk, oil, and vanilla until smooth.
Stir in the flour mixture with a wooden spoon until moistened.
Fold in the chocolate chunks.
Fill the prepared tins about 3/4 full. Reserve any leftover batter for a second batch. Bake for 20 to 23 minutes, or until the muffins have firm, rounded tops, and a toothpick inserted into the center of one muffin comes out with a few moist crumbs attached.
Set the pan on a wire rack to cool for 10 minutes.
Remove the muffins from the pan and let them cool on the rack for 5 minutes.
Make them disappear. You can keep them in an airtight container or in resealable plastic bags for up to 24 hours at room temperature or stash them in the freezer for up to 2 months.