Remove Greek yogurt from the fridge 15 minutes before starting.
Prepare the coffee, sweeten it if necessary and then pour it into a shallow bowl. Let cool for to room temperature before dipping the cookies.
Divide egg whites from egg yolks into 2 separate bowls and beat egg whites until stiff.
Add to the yolks granulated sweetener, Greek yogurt, and optionally marsala liquid. Gently whisk until smooth and creamy.
Gradually add to the mixture stiff egg whites and stir using a spatula; but be careful not to overmix it.
Spread one layer of cream over a rectangular dish. Quickly dip cookies into the coffee (without over-soaking them) and line over the cream. Cover with an additional layer of cream, sprinkle with cocoa powder and repeat the process with the second layer of cookies.
Refrigerate for 6 hours and sprinkle with cocoa powder before serving. If stored in the fridge in an airtight container, your tiramisu will last for up to 3 days.