Spring shells with cheese

Ingredients:

• 0.9 kg. medium zucchini
• 110 g butter
• 1/4 cup premium flour
• 0.5 tsp. grated nutmeg
• A pinch of cayenne pepper
• 6 cups whole milk
• 4 sprigs of fresh thyme
• 3 bay leaves
• Grated zest of half a lemon
• 450 g medium shell pasta
• 4 shallots, chopped
• 2 large egg yolks, lightly beaten
• 110 g grated Parmesan (about 1 cup)
• 110 g grated Gruyere (about 1 and 1/4 cups)
• 110 g of small spinach

Preparation:

1. Grate the zucchini coarsely into a colander. Toss with 1 tablespoon of salt, then place in the sink for about 15 minutes to drain. Squeeze out all the liquid.
2. Meanwhile, melt 4 tablespoons of butter in a large saucepan over medium heat. Add the flour, nutmeg, cayenne pepper, 2 tablespoons of salt, and black pepper to taste. Stir with a wooden spoon to form a paste. Cook, stirring, until the paste thickens slightly, about 3 minutes.
3. Slowly whisk in the milk, then add the thyme, bay leaf, and lemon zest and bring to a boil, stirring constantly. Reduce the heat and simmer until the liquid thickens slightly, about 25 minutes. Strain into a bowl, discarding the herbs.
4. Meanwhile, position a rack in the upper third of the oven and preheat the oven to 220°C (425°F). Bring a large pot of salted water to a boil; add the pasta and cook until al dente, about 8 minutes. Drain and transfer the shells to the sauce.
5. In a skillet over medium heat, melt the remaining 4 tablespoons of butter. Add the shallots and cook until translucent, 2-3 minutes. Add the zucchini and cook, stirring, until almost tender, about 4 minutes. Add the zucchini mixture to the pasta along with the egg yolks and most of the cheese, reserving 3 tablespoons for baking. Then add the spinach.
6. Transfer the mixture to a 22 x 32 cm baking dish and sprinkle with the remaining cheeses. Bake until golden brown, 25-30 minutes. Let rest for 10 minutes and serve.