Place pork belly, skin side up, in a baking dish. Refrigerate a minimum of 8 hours (or overnight).
Preheat the oven to 400°F (200°C).
Spread salt on top of pork belly skin in a thick layer. Add beer and soy sauce to the pan, avoiding the salt layer.
Roast pork for about 1 hour or until tender and skin has shrunk. Set aside.
Meanwhile, melt 1 tsp (15mL) of the butter in a large saucepan over medium heat and saute mushrooms until golden and tender. Remove to plate and set aside.
Return pan to medium-low heat and add remaining butter to melt. Add cream, Dijon, chili powder, thyme and petter, whisking to combine.
Increase heat to medium and bring the cream to a boil, stirring constantly.
Reduce heat to low and simmer for 5-7 minutes or until cream starts to thicken. Stir in half of the cheddar and all of the gouda, firm and Asiago cheeses as well as the mushrooms, stirring until cheese is smooth.
Add the cooked pasta and stir to coast. (If you haven't pre-cooked, add pasta to salted, boiling water and cook for about 4 minutes, stirring occasionally.)
Remove salt layer from pork and place under broiler for about 5 minutes or until the skin puffs up. (Careful not to burn the skin here, keep a close eye on the pork belly.)
Remove pork belly from dish and slice thinly. Discard salt and liquid mixture.
Scrape pasta and cheese mixture into a large baking dish and top with remaining cheddar cheese and pork slices.
Broil for about 3 minutes or until cheese is golden brown and bubbly.