Grease two small ramekins well with butter, and dust with cocoa powder until completely coated, tapping out the excess.

Preheat your oven to 425°F.

In a medium microwave-safe bowl, melt the butter and the two types of chocolate in 30-second intervals, stirring between each, until completely smooth.

In a small bowl, whisk together the eggs and vanilla.

In another small bowl, whisk together the powdered sugar, flour, salt, and espresso powder.

Add the egg mixture and the dry ingredient mixture to the melted chocolate, and gently fold everything together.

Switch to a whisk and gently whisk until the batter is smooth and thick like brownie batter.

Divide the batter between the two prepared ramekins or 6 muffin tin cavities.

Bake for 11 minutes for the ramekins, or start with 7-8 minutes for the muffin tin.

The sides of the cake should appear set while the center looks a bit underdone with a wet appearance.

Let the cakes cool for 1 minute before removing them from the ramekins.

Place a plate upside down over the top of the cake and flip the ramekin over.

Gently lift the ramekin straight up off the cake and enjoy immediately with desired toppings.

Wrap leftovers in plastic wrap or an airtight container and refrigerate for 2-3 days.

Reheat in the microwave in 15-second intervals until warm.