Preheat the oven to 350ºF.
Bring a large pot of salted water to a boil.
Combine the half and half, fontina and mustard powder in a heat-proof mixing bowl and place on top of the boiling water, double boiler-style.
Heat a sauté pan over medium-high heat and add the butter and prosciutto
When the prosciutto is crispy, add the onion and thyme and sauté until the onions become translucent.
Deglaze the pan with the wine and reduce until all liquid has evaporated and reserve.
When the cheese sauce is fully melted, remove the bowl from the pot and keep warm.
Cook pasta according to package instructions. Drain, rinse, and reserve.
Return the pasta to the pot. Add the cheese sauce and prosciutto mixture and combine thoroughly.
Transfer the pasta mixture to a baking dish. Top with the breadcrumbs and bake for 20-30 minutes, or until bubbly and golden brown.
When the pasta is done, garnish with the chopped parsley and serve hot.