Lightly grease two 6-ounce ramekins with butter or nonstick spray. Place them on a baking sheet. Set aside.

Preheat oven to 350°F (177°C).

Coarsely chop 2 ounces (57g) of semi-sweet chocolate. Reserve 1 ounce (28g) for step 5 (don’t chop). Combine the chopped chocolate and heavy cream in a medium heatproof bowl. Microwave in 20-second increments, stirring after each increment until melted and smooth. Whisk in the brown sugar until no lumps remain. Whisk in the oil, 2 Tablespoons of beaten egg, and vanilla extract until combined. Set aside.

In a small bowl, whisk the flour, baking powder, and baking soda together. Pour the dry mixture into the wet ingredients and fold with a silicone spatula until all of the ingredients are combined and there are no lumps. Pour evenly into the ramekins; they should be just about 3/4 of the way full.

Cut the remaining 1 ounce of chocolate in half. Place a piece of chocolate (0.5oz/14g) into the center of each filled ramekin and use a spoon to fully submerge the chocolate.

Bake for 15–17 minutes, rotating the baking sheet at the 8-minute mark.

Remove from the oven and serve immediately. The centers will be slightly gooey, with melted chocolate inside. Serve warm.