1️⃣ Preheat the oven to 375°F (190°C). Lightly grease a baking dish with olive oil or butter.

2️⃣ Prepare the potatoes: Wash and thinly slice the Yukon Gold potatoes (about ¼ inch thick). In a large bowl, toss the sliced potatoes with olive oil, salt, pepper, garlic powder, and rosemary until evenly coated.

3️⃣ Make the creamy sauce: In a small saucepan over medium heat, warm the heavy cream with minced garlic and Dijon mustard. Stir occasionally until fragrant and just starting to simmer. Remove from heat and mix in the Gruyère and Parmesan cheeses until melted and smooth. Season with salt and pepper to taste.

4️⃣ Assemble the bake: Layer half of the potatoes evenly in the baking dish. Pour half of the creamy sauce over the potatoes. Repeat with the remaining potatoes and pour the rest of the sauce on top.

5️⃣ Optional topping: Mix breadcrumbs with melted butter and sprinkle evenly over the top for a golden, crunchy finish.

6️⃣ Bake: Cover the dish with foil and bake for 40 minutes. Remove the foil and bake for an additional 20 minutes or until the potatoes are tender and the top is golden brown.

7️⃣ Garnish and serve: Let the dish cool slightly, then sprinkle with fresh parsley if desired. Serve warm as a delicious, hearty side or main.