Creating Zucchini Gratin with Yellow Squash is both fun and straightforward. Just follow these steps:

1. Preheat Oven: Preheat your oven to 375°F (190°C).
2. Prepare Baking Dish: Lightly grease a 9×13-inch baking dish with olive oil or cooking spray.
3. Sauté Onion and Garlic: In a skillet, heat olive oil over medium heat. Add diced onion and minced garlic, sautéing until translucent and fragrant, about 3-5 minutes.
4. Layer Vegetables: In the prepared baking dish, layer half of the sliced zucchini and yellow squash. Sprinkle lightly with salt, pepper, thyme, and oregano.
5. Add Cheese: Evenly distribute half of the mozzarella and half of the Parmesan cheese over the vegetable layer.
6. Repeat Layers: Create a second layer with the remaining zucchini and yellow squash, seasoning with salt and pepper, followed by the rest of the cheeses.
7. Add Cream: Pour heavy cream evenly over the top of the layers, ensuring all vegetables are coated.
8. Bake: Cover with aluminum foil and place in the preheated oven. Bake for 20-25 minutes.
9. Remove Foil and Finish: After 25 minutes, remove the foil and bake for an additional 10-15 minutes until bubbly and golden brown on top.
10. Garnish and Serve: Let cool slightly before serving. Optionally, garnish with fresh parsley for added color and flavor.

By following these straightforward steps, you’ll have an incredible Zucchini Gratin with Yellow Squash ready for enjoyment!