Step 1

In a medium bowl, whisk together the egg yolks and 1 tablespoon of sugar until smooth and pale yellow in color. Add the mascarpone and whisk until well combined, then whisk in the rum; set aside.

Step 2

In a medium bowl, combine the egg whites and the remaining 2 tablespoons sugar. With a hand mixer on medium-high, whip until they hold soft peaks when the beaters are lifted, 1 to 2 minutes; do not overwhip.

Step 3

With a silicone spatula fold about ⅓ of the whipped whites into the mascarpone mixture until just a few streaks remain. Fold in the remaining whites, taking care not to to deflate the mixture. Serve right away or cover with plastic wrap and refrigerate for up to 45 minutes. Dust with cocoa just before serving.