Spicy Fennel and Turmeric Béchamel Lasagna

Ingredients

• 2 tablespoons olive oil
• 2 fennel bulbs, diced
• 1 medium white or yellow onion, diced
• 2 tablespoons harissa
• 4 cloves garlic, minced
• 2 cups tomatoes, diced
• 1 cup tomato sauce
• 3 tablespoons butter
• 3 tablespoons flour
• 1/2 tablespoon turmeric
• 2 cups milk, warm
• 1/4 cup finely grated parmesan or other hard cheese (optional)
• Salt to taste
• 4 no-boil lasagna sheets
• 1 cup shredded mozzarella
• Fennel fronds for garnish