Preheat oven to 400 degrees F (205 degrees C).
In a pot, melt together the Butter (4 tablespoon) and Cooking Oil (2 tablespoon). Add the Onion (1) and cook for 3 minutes.
Add Garlic (1/2 teaspoon) and cook for 1 minute.
Add All-Purpose Flour (5 tablespoon). Cook, stirring constantly, until mixture comes together into a roux.
Add Milk (3 cup). Cook, stirring, until mixture starts to bubble and thicken. Remove from heat.
Add Colby & Monterey Jack Cheese (2 cup), Ricotta Cheese (1 cup), Sour Cream (1/4 cup), and remaining Butter (4 tablespoon). Stir to combine, then return to medium heat. Cook until sauce is melted together and creamy. Set aside.
Into a mixing bowl, add Egg (1). Quickly whisk it while adding 1/2 cup of the cheese sauce, then continue whisking for 30-45 seconds. Return to the pot of cheese sauce.
Add Salt (1 teaspoon), Ground Black Pepper (1 teaspoon), Herbes de Provence (1/2 teaspoon), Dried Parsley (1 tablespoon), and Dried Chives (1 tablespoon). Mix.
Add Pasta Shells (12 ounce). Mix well to coat.
Transfer pasta to a casserole dish. Sprinkle Shredded Cheese (1 cup) over top.
Bake for 30-45 minutes, until brown and bubbly on top.
Allow dish to cool for 15-20 minutes before serving.