Preheat the oven to 325 degrees F.

Brush softened butter in an upwards motion on the sides and bottom of a 6.4 oz ramekin.

In a small bowl, combine the butter and flour until it forms a cookie dough-like consistency. Set aside.

In a small saucepan over low-medium heat, bring the milk and 12g (1 tbsp) of granulated sugar to a simmer or about 190 degrees F. Remove from heat and quickly mix in the butter, flour mixture. Return the saucepan to medium heat and continue cooking while stirring constantly for 1-2 minutes or until thickened.

Transfer the mixture to a medium bowl and quickly whisk in the melted chocolate, espresso powder, and egg yolk. Set aside.

In a small bowl, beat the egg white with an electric mixer until it begins to foam. Gradually add in the remaining 18g (1 ½ tbsp) of granulated sugar, and whisk until stiff peaks form.

Using a rubber spatula, gently fold the meringue into the soufflé base in 3 additions.

Once all of the meringue has been combined and no more streaks of white remain, transfer the batter to a piping bag. Snip off the tip of the bag and pipe it neatly into the prepared ramekin.

Place the ramekin on a small baking sheet and bake the soufflé for about 20 minutes or until well risen the top appears matte. Do NOT open the oven while it bakes, or it may deflate.

Dust the chocolate soufflé with cocoa powder and enjoy immediately!