Preheat your oven to 375°F (190°C) and lightly grease a 9x13 inch baking dish.

In a large saucepan, melt the butter over medium heat and sauté the minced garlic until fragrant, about 1 minute.

Whisk in the flour and cook for 2 minutes to create a roux, stirring constantly to ensure the garlic doesn't burn.

Gradually pour in the milk and heavy cream while whisking vigorously to ensure a smooth, lump-free texture.

Simmer the sauce on low heat until it thickens enough to coat the back of a spoon, then stir in the nutmeg, salt, and black pepper. Remove from heat.

In a medium bowl, mix the ricotta cheese with the chopped fresh spinach and a pinch of salt.

Spread a thin layer of the white sauce on the bottom of the prepared baking dish.

Place 3 lasagna noodles over the sauce, then spread half of the ricotta-spinach mixture over the noodles.

Ladle about 1 cup of sauce over the ricotta layer and sprinkle with 1/3 of the mozzarella cheese.

Repeat the layering process: 3 noodles, remaining ricotta-spinach mixture, sauce, and another 1/3 of the mozzarella.

Top with the final 3 noodles, pour the remaining white sauce over everything, and cover with the remaining mozzarella and parmesan cheese.

Cover the dish tightly with foil and bake for 25 minutes.

Remove the foil and bake for another 15-20 minutes, or until the cheese is bubbly and golden brown.

Let the lasagna rest for at least 10 minutes before slicing to allow the creamy layers to set.