Preheat oven to 325°F. Toast bread in hot oven to golden brown. Pulse the bread in food processor to make fresh, large breadcrumbs.
Using the tip of a very sharp paring knife, remove the core of the Brussels sprouts and separate leaves. You should yield 3 cups loosely packed leaves.
Bring a large pot of water to a boil. Salt water.
Peel the potato and cut into thirds horizontally, then slice the thirds of potato across lengthwise, into about 1/4-inch slices. Boil potatoes 5 minutes, add Brussels sprouts leaves after 2 minutes. Remove potatoes and cabbage from water with a spider or strainer and transfer to a serving bowl.
Cook pasta in boiling water to al dente in the same water. Reserve a little starchy cooking water just before draining.