Put the mascarpone cheese, egg yolk, and yogurt in a large bowl, and beat together until smooth.

Whisk the egg white in a separate, spotlessly clean, grease -free bowl until stiff but not dry, then whisk in the sugar and gently fold into the cheese mixture.

Divide half the mixture between 4 sundae glasses.

Mix the Rum and coffee together in a shallow dish. Dip the Ginger Snaps into the rum mixture, then break them in half, or into smaller pieces if necessary, and divide between the glasses.

Stir any remaining coffee mixture into the remaining cheese mixture and divide between the glasses.