Preheat your oven to 350°F (175°C).

Lightly coat each ramekin with cooking spray, then dust the insides with granulated sugar if desired.

In a medium bowl, whisk together the powdered sugar, cocoa powder, and flour until well combined.

In a small saucepan, combine the low-fat milk and water over medium heat until it simmers, then add to the dry mixture, stirring continuously.

In a separate bowl, whip the egg whites with cream of tartar until soft peaks form; gradually add 3 tbsp granulated sugar until stiff peaks form.

In another bowl, whisk the egg yolks and vanilla extract, then gently fold into the chocolate batter.

Gently fold the whipped egg whites into the chocolate batter in three additions.

Evenly divide the soufflé batter among the prepared ramekins, filling them about three-quarters full.

Bake for about 20 minutes until puffed up and slight jiggle in the center.

Remove from oven, dust with powdered sugar, and serve immediately.