In a small bowl, whisk together the sugar, flour, and cocoa powder.
Stir in the egg yolk, vanilla, and melted butter until smooth.
Fold in the chocolate chips.
Lightly butter a 10-ounce ramekin and pour in the batter, spreading evenly.
Place ramekin on a baking sheet and bake at 350°F for about 30 minutes.
Let cool for about 5 minutes before enjoying. Eat as-is or topped with vanilla ice cream.
Notes
Use quality chocolate: Choose good chocolate chips or bars for richer flavor. Ghirardelli, Guittard, and Scharffen Berger are excellent; Trader Joe’s and 365 by Whole Foods are great budget options.
Measure flour correctly: Spoon and level the flour instead of scooping to avoid dry or cakey brownies.
Don’t overmix: Stir just until combined to keep the brownie soft and fudgy.
Avoid overbaking: Bake about 30 minutes. The brownie will continue to set as it cools, giving you a moist, gooey center.