Preheat oven to 400F.
Prepare the breadcrumb topper: Cut the bulb of garlic across the top end to expose all of the cloves then dress with a drizzle of EVOO, about 2 tablespoons, salt and pepper. Wrap bulb in foil and roast until tender and caramel in color, 40 minutes. Squeeze out the roasted garlic cloves from the skins and smash with the back of the knife into a pure.
While the roasted garlic is roasting, toast up the breadcrumbs in a large skillet over medium heat with remaining EVOO, remove to large mixing bowl.
Add the roasted garlic, Parmigiano-Reggiano cheese and parsley to the toasted breadcrumbs. Reserve.
Lower oven heat to 350F.
Bring a large pot of water up to a boil and cook penne 2 minutes shy of al dente. Drain and set aside.
Meanwhile, melt 4 tablespoons butter in a large skillet over medium heat. Add onions, thyme and bay leaf, and season with salt and pepper. Stir occasionally for 30 minutes until onions are caramel in color, and very soft and sweet. Deglaze the pan with white wine and discard bay leaf.
While onion is cooking, heat another large skillet over medium-high heat with EVOO, Add chicken sausage, cook until golden brown, 7-8 minutes.
Put a large pot over medium heat and melt remaining 2 tablespoons butter. Add the flour and cook for about a minute, or until fragrant. Add milk to the flour mixture and whisk until it's thickened and smooth. Stir in the shredded cheeses and mix until melted. Season to taste with salt, black pepper and nutmeg.
Stir in the pasta, caramelized onions, cooked crumbed chicken sausage and mix well. Pour the mac 'n' cheese into a baking pan and top it with the reserved breadcrumb topping. Bake the mac 'n' cheese until it is warmed through, about 8-10 minutes. Serve immediately.