1. Coat a 2- to 2 1/2-quart baking dish with cooking spray.
2. Heat oven to 350°.
3. Cook the macaroni in boiling salted water, under-cooking slightly, otherwise the end result of the casserole will yield mushy, overcooked pasta. Not good. So, if the pasta is supposed to cook for 8 minutes, I'll cook it for about 6 and a half minutes.
4. Drain and rinse the macaroni with cold water; set aside and let drain some more.
5. Cut the vidalias in half and slice into thin strips. Slice the shallot thinly.
6. In a large skillet, melt 2 tablespoons of butter over medium-high heat. Toss in the sliced onions and shallots, and cook for 3 minutes, stirring to coat. Reduce the heat to medium-low and let cook slowly until nicely browned, slightly caramelized.
7. Pour in the white wine and let cook down. Add the chopped garlic and season with salt and pepper. Once the liquid has all been absorbed, remove from the heat and set aside.
8. Peel a small vidalia onion and cut in half, removing the root.
9. Pour the milk and cream into a microwave safe bowl or measuring cup. Add the bay leaf and the halved onion and scald in the microwave) about 2-3 minutes on high). Remove the onion and bay leaf.
10. In a large saucepan, melt 2 tablespoons of butter over medium-low heat. Add the flour and stir until well blended and bubbly. Season with a bit of salt and pepper, and them pour in the milk and cream mixture, whisking constantly.
11. Cook, stirring, until thickened. Add the mustard and hot sauce, stirring well and tasting to check the seasoning.
12. Fold in the boursin cheese, and cheddar. Cook, stirring, until cheeses have melted.
13. Dump the drained macaroni into the prepared baking dish. Add the caramelized onions and mix well.
14. Pour in the cheese sauce and stir to make sure everything is evenly distributed and coated.
15. Sprinkle the bread crumbs over the casserole and top with grated cheddar and parm. Sprinkle with paprika.
16. Bake for 20 to 25 minutes, until the cheese sauce is bubbly and topping is lightly browned.