Bring a pot of Water (8 cup) with Salt (2 tablespoon) to a boil. Cook Gluten-Free Elbow Macaroni (6.5 ounce) for 9 minutes. Drain and set aside.
Preheat oven to 425 degrees F (218 degrees C).
Into an oven-safe pan, add Salted Butter (3 tablespoon) and Shallot (1/4 cup). Once butter is melted and bubbling, add 1 cup of Milk (1 cup) and Heavy Cream (1 cup). Bring to a boil.
In a bowl, whisk together Milk (1/4 cup) and Corn Starch (2 tablespoon). Add to the pan and whisk to combine. Turn off heat.
Add 2 cups of the Shredded Extra Sharp Cheddar Cheese (2 cup), Salt (3/4 teaspoon), and Dry Mustard (1/2 teaspoon). Stir to combine.
Add Ricotta Cheese (1/4 cup) and the pasta. Stir well to coat.
Sprinkle the top of the dish with remaining Shredded Extra Sharp Cheddar Cheese (1/2 cup). Add Tomato (5 slice). Sprinkle with Grated Parmesan Cheese (1/4 cup) and Dried Parsley (to taste).
Bake for 30-45 minutes, or until top is brown and bubbly.
Serve warm right out of the skillet.