Preheat the oven to 350°F (175°C).
Prepare the chocolate cake batter according to the package instructions.
Grease individual ramekins and fill them halfway with the cake batter.
Place a piece of chocolate in the center of each ramekin.
Cover the chocolate with more cake batter until the ramekins are three-quarters full.
Bake for 12-15 minutes, or until the edges are set but the center is still slightly jiggly.
Remove from the oven and let cool for a few minutes.
Carefully invert each ramekin onto a plate.
Serve warm with a scoop of vanilla ice cream.