Pre-heat the oven to 425 degrees. Butter six 4-ounce ramekins. Line the bottom of each ramekin with a circular piece of parchment paper and butter the parchment. Sprinkle each ramekin with sugar, shake it around to coat the inside and toss the excess sugar. Place the ramekins on a sheet tray or rimmed baking sheet and set aside.

In a medium saucepan, bring the granulated sugar, milk and espresso powder to a rolling boil. Whisk in the tablespoon of flour and continue to rapidly mix the ingredients together for another minute. Remove the saucepan from the heat and add the chopped chocolate, stirring while it melts. Add in the butter and continue to mix until smooth. Add the egg yolks one at a time and whisk until incorporated. Set aside the chocolate mixture.

In a clean, dry bowl, beat the egg whites on medium-high speed until they hold a stiff peak. Gently fold together the egg whites with the chocolate mixture, until just combined. Divide the batter evenly among the 6 ramekins. Arrange the ramekins on the rimmed baking sheet and place into the oven. Bake the cakes for 12-15 minutes. The cakes will rise and be dry around the edges when they are done. Remove the sheet tray of ramekins from the oven and run a knife around the edge of each ramekin to release the cake. Carefully invert them on a plate, remove the parchment paper rounds and sprinkle with confectioners’ sugar. Serve hot!