Spinach gratin

Ingredients:

• 55 g unsalted butter
• 4 cups chopped onion (2 large onions)
• 1/4 cup flour
• 1/4 tsp. grated nutmeg
• 1 cup heavy cream
• 2 cups of milk
• 1.4 kg frozen chopped spinach, thawed (5 packages at 280 g)
• 1 tbsp. freshly grated parmesan
• 1 tbsp coarse salt
• 0.5 tsp freshly ground black pepper
• 0.5 cups grated Gruyere

Preparation:

1. Preheat oven to 220°C.
2. Melt the butter in a heavy-bottomed skillet over medium heat. Add the onion and cook until translucent, about 15 minutes.
3. Add flour and nutmeg and cook, stirring, for another 2 minutes. Add cream and milk and cook until the mixture thickens.
4. Squeeze as much water as possible from the spinach and add it to the sauce. Add 0.5 cups of Parmesan and mix well. Season with salt and pepper to taste.
5. Transfer the spinach to a baking dish and sprinkle with the remaining 1/2 cup Parmesan and Gruyère. Bake for 20 minutes, until the gratin is heated through and bubbly. Serve hot.