You will need two 6-ounce ramekins.
- 6 tablespoons (1¾ ounces) all-purpose flour
- ¼ teaspoon baking powder
- ⅛ teaspoon baking soda
- ⅛ teaspoon salt
- 3 ounces bittersweet chocolate (2 ounces chopped, 1 ounce broken into two ½-ounce pieces)
- ¼ cup whole milk, room temperature
- 3 tablespoons packed light brown sugar
- 2 tablespoons vegetable oil
- 2 tablespoons lightly beaten egg, room temperature
- ¼ teaspoon vanilla extract
1. Adjust oven rack to middle position and heat oven to 350 degrees. Grease and flour two 6-ounce ramekins. Whisk flour, baking powder, baking soda, and salt together in bowl.
2. Microwave 2 ounces chopped chocolate and milk in medium bowl at 50 percent power, stirring occasionally, until chocolate is melted and mixture is smooth, 1 to 3 minutes. Stir in sugar until dissolved; let cool slightly. Whisk in oil, egg, and vanilla until combined. Gently whisk in flour mixture until just combined. Give batter final stir with rubber spatula.
3. Divide batter evenly between prepared ramekins and gently tap each ramekin on counter to release air bubbles. Wipe any drops of batter off sides of ramekins. Gently press 1 square chocolate into center of each ramekin to submerge. Place ramekins on rimmed baking sheet and bake cakes until tops are just firm to touch and center is gooey when pierced with toothpick, about 15 minutes, rotating sheet halfway through baking. Let cool for 2 to 3 minutes before serving in ramekins.