Bring a large pot of lightly salted water to the boil. Add pasta and cook for 8 to 10 minutes or until al dente; drain and lay lasagne sheets on kitchen towels.
Meanwhile, in a large frying pan over medium heat, cook sausagemeat, spicing to taste, until no longer pink. Set aside.
In a large bowl, mix the ricotta and 2/3 of the pasta sauce. In a medium bowl, mix the Parmesan and mozzarella cheeses.
Stir all but 125g of the cheese mixture into the ricotta mixture; stir in the sausagemeat and chopped spinach.
Preheat oven to 220 C / Gas 7.
Coat the bottom of a 20x30cm baking dish with a thin layer of pasta sauce. Lay 3 to 4 lasagne sheets lengthways and side by side; then lay 3 to 4 lasagne sheets overlapping and in a staggered pattern on top.
Add a generous layer of the sausage/cheese; repeat layers twice, until they have reach 1.25cm from the top of the baking dish. Layer lasagne sheets on top of the lasagne and coat in the remaining pasta sauce. Cover with remaining cheese mixture and bake in preheated oven for 45 minutes or until golden brown.