1. Cook the Shells: Start by boiling the jumbo pasta shells according to the package directions until they are al dente. Drain the shells and rinse them with cool water to stop the cooking process.

2. Cook the Mushrooms: In a large skillet, heat the olive oil and butter over medium heat. Add the minced garlic and cook for about 30 seconds, just until fragrant. Then, stir in the finely chopped mushrooms and cook for 6 to 8 minutes, until the mushrooms are softened and lightly browned. Season with a pinch of salt and pepper.

3. Make the Filling: In a mixing bowl, combine the sautéed mushroom mixture with the ricotta cheese, half of the mozzarella, half of the Parmesan, dried basil, dried oregano, and red pepper flakes (if using). Stir everything together until well-incorporated.

4. Make the Sauce: Using the same skillet, add the heavy cream and whole milk. Simmer the sauce for 4 to 5 minutes, stirring occasionally, until it has thickened slightly. Then, stir in the remaining Parmesan cheese. Taste and season with additional salt and pepper as needed.

5. Assemble and Bake: Preheat your oven to 375°F. Spread a small amount of the cream sauce in the bottom of a baking dish. Carefully fill each cooked pasta shell with the mushroom and cheese mixture, then arrange the stuffed shells in the prepared baking dish. Pour the remaining cream sauce over the top of the shells, then sprinkle with the remaining mozzarella cheese. Cover the dish with foil and bake for 20 minutes. Then, remove the foil and continue baking for an additional 10 to 15 minutes, until the sauce is bubbly and the cheese is melted and golden brown.

6. Serve and Enjoy: Finally, garnish the Creamy Garlic Mushroom Stuffed Shells with freshly chopped parsley. Serve the dish warm, and get ready for your taste buds to be transported to a culinary paradise!