The Ultimate Lasagna

Ingredients

• 1/4 cup extra-virgin olive oil
• 2 medium onions, finely chopped
• 4 ribs celery, finely chopped
• 2 carrots, finely chopped
• 5 cloves garlic, sliced
• 1 pound ground veal
• 1 pound ground pork
• 4 ounces pancetta or slab bacon, run through the medium holes of the butcher’s grinder
• one 6-ounce can tomato paste
• 1 cup whole milk
• 1 cup dry white wine
• 1 teaspoon fresh thyme leaves
• salt and freshly ground black pepper
• 1 cup packed fresh spinach
• 5 large eggs
• 3 1/2 cups all-purpose flour, plus more for kneading
• 5 tablespoons unsalted butter
• 1/4 cup all-purpose flour
• 3 cups whole milk
• 2 teaspoons salt
• 1/2 teaspoon freshly grated nutmeg