Place all ingredients into a large bowl. Initially, work through the ingredients with your fingers to distribute evenly, then start working with the heel of your hand, incorporating dry ingredients into mascarpone/egg white to bind. This will take nearly 5 minutes - so don't give up! And don't worry about keeping the rice krispies whole, just smush right down on those babies and work the dough!
Separate the dough into 2 pieces and shape each piece into a firm, 6-inch log. Roll up tightly in plastic cling film and refrigerate a minimum of 4 hours before proceeding with recipe.
Preheat oven to 400°F Line a baking sheet with parchment paper.
Remove first roll of dough. With a sharp knife, cut the dough log into 1/4-inch-thick slices (no thicker!). Place slices on baking sheet and bake in the middle rack of the preheated oven for 18-20 minutes. Repeat with second pan, if necessary. When done baking, place both pans in oven, staggering one up, the other low down, and leave in hot, turned-off oven for another 40 minutes. This will ensure you have a nice, dry, crisp wafer, with a rich, brown colour.
Remove and allow to cool completely. Store in an airtight container.