In a small microwave-safe bowl, melt the chocolate and butter. Stir together until smooth.
In a medium bowl, stir together the flour, cocoa powder, powdered sugar, and salt. Add the egg and vanilla extract and mix until combined. Add the chocolate mixture and mix until uniform.
Grease two ramekins and split the batter between them. Place on a baking sheet and bake for 12-14 minutes. Do not overbake.
Cool for 1 minute, then turn out onto a plate. Best served with a scoop of ice cream.