1. Preheat oven to 350°F (175°C). Line a standard 12-cup muffin pan with paper liners.

2. Melt butter in a saucepan over medium heat. Remove from heat once melted.

3. Whisk in sugar, cocoa powder, and salt while the butter is still warm.

4. Let the mixture cool for 2 to 3 minutes.

5. Add eggs one at a time, whisking well after each egg.

6. Stir in vanilla extract.

7. Gently fold in flour until just combined.

8. Fold in chocolate chips.

9. Fill each muffin liner about ¾ full.

10. Bake for 18 to 22 minutes, until tops are crackly and a toothpick comes out with moist crumbs.

11. Cool in the pan for 10 minutes, then transfer to a wire rack.

12. Dust with powdered sugar or top with chocolate shavings before serving.