Lasagna Bolognese with Béchamel Sauce

Ingredients

• 3 tbsp extra-virgin olive oil
• 1 large onion, finely diced
• 1 medium carrot, peeled and finely diced
• 1 stalk celery, finely diced
• 1 1/2 lb ground beef, lean
• 2 tbsp tomato paste
• 1 1/2 tsp salt
• 1/4 tsp black pepper, freshly cracked
• 1 tsp dried oregano
• 1/2 tsp paprika
• 1 cup beef stock, hot
• 1 3/8 L (46 oz) passata or crushed tomatoes
• 4 sprigs fresh thyme
• 1 tbsp brown sugar
• 1 cup milk, warmed
• 1/2 cup unsalted butter
• 1/2 cup + 3 tbsp all-purpose flour
• 4 cups milk, full fat
• 1 tsp salt
• 1/4 tsp white pepper
• 1/4 tsp grated nutmeg
• 8-10 fresh lasagna sheets
• 200 g Parmigianino-Reggiano or parmesan, grated
• chives or parsely, finely chopped