To make the Mornay Sauce: In a saucepan over low to medium heat, melt 3 tbsp butter completely then add the flour. Whisk until it forms a paste-like consistency and continue to cook until yellowish or light brown creamy color. Add milk and whisk until the sauce thickens. Careful not to bring to a boil. Put in the cloves and the onion, making sure they’re distributed evenly. Add this together with the bay leaf, and nutmeg to the sauce and cook for another 10 minutes. Adjust consistency by adding a little bit of milk or water if the sauce turns too thick. Strain sauce to remove onions and herbs then return to heat. Add grated Parmesan cheese and grated Gruyere cheese and mix until melted. Set aside.
To build the sandwich: Start with layering bread, cheese slice, SPAM® Less Sodium slices, cheese slice, and bread.
Melt a knob of butter in a pan over low to medium heat. Toast the sandwich on both sides until crisp, golden brown, and the cheese has melted.
Transfer to a serving plate and carefully pour a generous spoonful of the mornay sauce.