Pre-heat oven to 350°F.
Grease a 9 x 13-inch baking dish with butter.
In a large bowl, mix the Cheddar and mozzarella; set aside.
In a small bowl, whisk the evaporated milk, egg, tomato paste, garlic and onion powders, mustard, thyme, Scotch bonnet pepper, 1 teaspoon salt, and a generous pinch of black pepper until very well blended.
Cook macaroni, in boiling salted water, according to the package directions for al dente; drain and return to the pot.
Stir in the tablespoon of butter until melted; add half the cheese and stir until it’s fully combined and starting to melt.
Stir in the milk mixture until the pasta is evenly coated.
Pour the pasta into the buttered dish; spread evenly and sprinkle the rest of the cheese on top.
Place in the oven and bake until the top is bubbling and golden brown; 35 to 40 minutes.
Remove from the oven and let rest for at least 10 minutes to help firm up.
The dish can be made up to a day in advance, tightly covered with foil or plastic wrap, and refrigerated, or cut into serving sizes, wrapped tightly and frozen.
Re-heat, covered with foil, in a 350°F oven or in a covered skillet on the stove.