Potato, Sausage, And Spinach Breakfast Casserole

Ingredients:

• 16 large eggs
• 1 1/4 cups heavy cream
• 1 1/2 teaspoons kosher salt plus more
• 3/4 teaspoon freshly ground black pepper plus more
• 5 tablespoons unsalted butter, divided
• 12 ounces fresh breakfast sausage links
• 2 cups sliced leeks, white and green parts only
• 2 russet potatoes (1 1/2 lb.), peeled, shredded, and lightly squeezed
• 1 pound frozen spinach, thawed, squeezed dry, roughly chopped
• 1 1/2 cups (4 oz.) grated Gruyère
• 1/2 cup (1 1/2 oz.) grated Parmesan

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