Preheat your oven to 375°F (190°C) and line a muffin tin. This is not the step to skip. Cold ovens ruin dreams.
Whisk the dry ingredients—flour, cocoa powder, baking powder, baking soda, salt, and both sugars—in a large bowl. Break up any cocoa lumps like you mean it.
Mix the wet ingredients in another bowl. Whisk the eggs, milk, oil, and vanilla until smooth and friendly-looking.
Pour the wet ingredients into the dry and gently stir. Stop when you don’t see dry flour anymore. Overmixing = tough muffins, and nobody asked for that.
Fold in the chocolate chips if you’re using them. Highly recommended behavior.
Divide the batter evenly into the muffin cups. Fill them about ¾ full for nice domed tops.
Bake for 18–22 minutes, until a toothpick comes out with a few moist crumbs. Not wet batter. Not bone dry.
Cool slightly, then eat one while standing in the kitchen like a champion.