Make bechamel sauce first. In a small saucepan add milk, celery, onion, bay leaves, peppercorns, carrot, parsley stalks on low heat and bring to simmer. Turn off heat and set aside to infuse for 10 minutes, then strain in a fine strainer to retain just the milk.
In a medium saucepan on low heat add the butter. Add the flour and stir for a minute, ensuring you don't burn the mixture. Then gradually add the milk a bit at a time, whilst stirring continuously with a wooden spoon. When possible change to a whisk and continue whisking until all milk is added. Increase to medium heat and whisk until thickened and creamy. Add cracked black pepper and salt to taste. Set aside to cool.
Preheat oven to 200 celcius. In a large non-stick pot on high heat the oil until hot. Add the onion, garlic, mince and mushrooms and cook for 4 minutes until meat is browned. Add the rest and stir bringing to boil. Reduce heat to low and simmer covered for 10 minutes.
In a 20cm square baking dish add a generous layer of the beef sauce then lasagna, then bechamel, then beef mix, then a mix of cheeses, then lasagna and repeat. Final layer should be lasagna, beef then bechamel. Scatter with parsley and top with most of the tasty cheese and then parmesan cheese and freshly cracked black pepper.
Bake for 40 minutes. Bon appetit
Notes & Tips
I used gluten free instant lasagne and rice flour in my bechamel sauce so that it was completely gluten free and absolutely delish.