Preheat oven to 450˚F. Grease 4 ramekins and dust with cocoa.
In a medium bowl, melt butter and chocolate at 2, 30 second intervals, stirring in between until just melted. Microwave 20 seconds more only if needed.
Add boiling water to espresso powder. Stir into chocolate mixture. Set aside and cool.
In a small bowl, whisk eggs and sugar together very well.
Whisk chocolate mixture and slowly add to the egg mixture in a steady stream.
Fold in flour to chocolate egg mixture only until just combined.
Distribute evenly into prepared ramekins. Set ramekins on a bake sheet.
Bake for 9 minutes, remove. Cool just slightly, then use a flat blade knife to cut around the sides of each ramekin. Invert a serving plate on top of ramekin, then flip it over. Carefully remove ramekin.
Garnish with a dusting of powdered sugar, berries, or ice cream and serve immediately.