Preheat oven to 425°F. Spray two 6-ounce ramekins with nonstick cooking spray and place on a baking sheet. Set aside.
1
To melt and smooth the butter and semi-sweet chocolate, microwave in 20-30 second increments in a large microwave-safe bowl, stirring well after each increment.
2
Whisk the powdered sugar until well combined after removing from the microwave, then add the egg, egg yolk, and vanilla and mix until combined.
3
Stir in the flour and espresso powder without overmixing. Split the batter between the two ramekins.
4
For 12–14 minutes at 425°, bake until edges are firm and center is slightly soft. Wait 1 minute after removing from oven. Carefully invert each ramekin onto a small plate, serve, and enjoy!