Preheat your oven to 350°F (175°C). Prepare a standard muffin tin by lining it with 12 muffin liners.
In a large mixing bowl, add the melted unsalted butter and sugar. Whisk together until the mixture is well combined and glossy.
Add in the eggs and vanilla extract. Whisk again until fully incorporated, creating a rich mixture.
In a separate bowl, sift together the all-purpose flour, cocoa powder, baking powder, and salt.
Gradually add the dry mixture to the wet ingredients. Whisk until just blended, being careful not to overmix.
Switch to a spoon and fold in the semi-sweet chocolate chips, scraping the bowl to ensure even mixing.
Divide the batter among the prepared muffin cups, filling each about three-quarters full.
Bake for 25 to 30 minutes, checking for doneness with a toothpick.
Allow the muffins to cool in the pan for a few minutes, then transfer to a wire rack to cool completely.
