I make the butternut squash lasagna too but with sage and hazelnuts or walnuts, depending on what I've got on hand. It takes a while so not necessarily every weeknight but it's a good recipe for the freezer or for a special weekend or party because you can make the filling and sauce a day or two ahead of time and then just assemble and bake the day of.
Preheat oven to 220c/gas 7.
Chop an onion and fry till pale gold (10 min). While it's cooking, peel and seed a butternut squash and cube into 1cm pieces - this recipe works best with a biggish squash that weighs at least 1kg. Add squash, 2 cloves crushed garlic, salt and pepper and cook, stirring occasionally, until squash is just tender (15 min).
While squash is cooking, make a white sauce: fry 2 cloves crushed garlic in a large slice of butter (prob about 50g) in a saucepan over low heat, then whisk in 75g plain flour and cook until it smells nutty (about 3 min). Add 800ml milk in a stream (you can add more milk if you think it's too thick). Add a bay leaf, bring to a boil, whisking constantly, then reduce heat and simmer 10 min until thick. Add salt and pepper and set aside to cool.
When the squash is tender, stir in a big handful flat leaf parsley (use scissors to snip over the squash), a palmful of ripped fresh sage leaves, and a big handful of chopped and toasted nuts - we often use a mix of whatever bits we've got in the cupboard - pecans, hazelnuts, walnuts, pine nuts etc. Set aside to cool.
(At this point you can put the filling and sauce separately in the fridge if you want to make this a day or two ahead - just bring back to room temp before assembling).
Mix together 100g grated parmesan and 225 grated mozzarella together. Spread a thin even layer of white sauce in a buttered lasagna dish and cover with pasta sheets, leaving spaces between sheets. Spread with more sauce, one third of squash filling, then two handfuls cheese. Repeat layering 2 more times, (pasta sheets, sauce, squash, cheese). You should be out of squash by now so top with remaining pasta, remaining sauce, and remaining cheese.
(At this point you can freeze it all assembled, then just defrost before baking.)
Tightly cover with foil (butter foil if you can be bothered - I never do) and bake in middle of oven 30 minutes, then remove foil and bake until golden and bubbling, 10 to 15 minutes more.
You need to let it stand for at least 10 min after it comes out of the oven to let the sauce thicken up a bit - otherwise it goes everywhere when you try and serve and it's so molten it will burn your mouth...