Add the chocolate, butter, espresso powder, water, and vanilla to a bowl. Place over a small pot of simmering water, and stir occasionally until fully melted and combined.
Beat the egg whites with an electric mixer until it begins to foam. Gradually add in the sugar, and whisk until stiff peaks form. Add to the melted chocolate mixture, and whisk quickly until fully combined.
Pour into the prepared ramekin and place on a small baking sheet. Bake the mini soufflé at 375 degrees F for about 18 minutes or until it has risen and the top has cracked and appears set.