Blanch the Savoy cabbage leaves in salted boiling water for about 5 minutes. The cabbage should still be crunchy. Cool cabbage leaves in a bowl of cold water, then pat them dry with paper towels.
Arrange half of the leaves on a board in one layer, but slightly overlapping to form a solid rectangle. Place prosciutto slices atop the cabbage. Top with another cabbage rectangle and another prosciutto layer. Starting from the narrower side, roll up the layers of cabbage and prosciutto quite tightly. Once they are completely rolled up, wrap the roll in plastic film and refrigerate for at least 1 hour.
Then unwrap and use a very sharp knife to cut this cabbage/prosciutto roll into 1/2 inch slices. (A very sharp knife is necessary to make clean slices.) Place a small piece of sliced prosciutto on each bread square and top it with a slice of cabbage-prosciutto roll. Top each canape with a leaf of Italian parsley.
