Preheat oven in 425°F.
Butter 9 x 13-inch glass baking dish.
Sauté bacon in heavy large nonstick skillet over medium heat until crisp.
Using slotted spoon, transfer bacon to paper towels and drain.
Remove all but one tablespoon bacon fat from skillet.
Add garlic in skillet and sauté until golden, about 3 minutes. Remove from heat.
Whisk cream, half and half, yolks and nutmeg in heavy medium saucepan to blend.
Add 1½ cups cheddar cheese, 1½ cups Fontina and the Parmesan and stir over medium-low heat until melted and smooth, about 5 minutes. Do not boil.
Stir in bacon and garlic. Remove from heat.
Cook pasta in pot of boiling salted water until tender but still firm in bite. Drain and transfer to prepared baking dish.
Pour sauce over pasta and stir until coated.
Sprinkle with remaining ½ cup cheddar cheese and remaining ½ cup Fontina.
Bake until sauce bubbles and top is brown, about 15 minutes.
Melt butter and mix in cracker crumbs.
Sprinkle macaroni and cheese with crumbs, and broil until crumbs are golden brown, about 2 minutes.