Crisp up the pancetta, set aside.
Brown the beef mince in the same pan until it sizzles and colours.
Add onion, carrot, celery, garlic, and pancetta back in.
Sweat for a few minutes.
Stir through the tomato purée, cook for 2 mins, then pour in the red wine.
Let the alcohol evaporate.
Add beef stock, tomatoes, bay leaves (and parmesan rind if you have).
Simmer gently for 1 hour.
For the béchamel: melt butter, stir in flour, cook for 2 mins.
Slowly whisk in milk until smooth, then melt through the Boursin.
Season to taste.
Build the lasagne: ragu → sheets → béchamel → mozzarella.
Repeat layers.
Bake at 200°C/400°F for 35 minutes until bubbling and golden.
Rest 15–20 minutes before slicing.
