1. In a large mixing bowl, beat egg whites until frothy, gradually adding sugars until a shiny, stiff snow forms.
2. Add the vanilla sugar, coffee, whipped topping, and the egg yolks, and beat until the mixture is stiff.
3. Gently stir in the crushed chocolate-coated pretzels by hand.
4. Pour ice cream into a container and freeze until firm, at least 24 hours.