Step 1: Preheat the Oven

Preheat your oven to 375°F (190°C) and grease a 9×13 inch baking dish with butter or non-stick spray.

Step 2: Prepare the Potatoes and Zucchini

Thinly slice the zucchini and potatoes using a mandoline slicer or a sharp knife. The slices should be about 1/8 inch thick to ensure even cooking.

Step 3: Sauté Garlic and Onion

In a medium skillet, heat 2 tablespoons of olive oil over medium heat. Add the onion and garlic, cooking until soft and fragrant (about 3-4 minutes). Remove from heat and set aside.

Step 4: Layer the Vegetables

In your greased baking dish, start by arranging a single layer of potato slices on the bottom. Sprinkle the top with a pinch of salt, pepper, and a little of the sautéed onion-garlic mixture. Add a layer of zucchini slices on top, seasoning again with salt, pepper, and the onion-garlic mixture.

Step 5: Add Parmesan and Repeat

After each layer of zucchini and potato, sprinkle a generous handful of Parmesan cheese. Repeat the layering process until all vegetables are used, finishing with a final layer of Parmesan on top.

Step 6: Make the Cream Mixture

In a small bowl, whisk together the heavy cream, thyme, and oregano. Pour this mixture evenly over the layered vegetables in the casserole dish.

Step 7: Top with Cheese and Bake

Finish the casserole by sprinkling the mozzarella cheese evenly across the top. Cover the dish with foil and bake in the preheated oven for 40 minutes.

Step 8: Remove Foil and Finish Baking

After 40 minutes, remove the foil and continue baking for an additional 15-20 minutes or until the top is golden brown, and the vegetables are tender. If you want an extra-crispy crust, you can broil the casserole for the last 2-3 minutes of cooking.