From a recipe by Yotam Ottolenghi, I found a way to ensure that non pre-cook lasagne was properly cooked (as I wrote here). Before that, I had always blanched the pasta sheets before assembling the pasta.
However, last Saturday in the Guardian Ottolenghi gave a recipe for mushroom lasagne, and told us to pour boiling water on to the sheets, leave them for two minutes, and dry them on a tea towel.
This is a very bad idea. The sheets will stick together, and you will have trouble prising them apart.
Use the dry sheets, breaking them up as necessary to fit them in the dish. As I wrote in the earlier entry: cover the dish, after you have assembled the lasagne, with foil, and cook for 30 minutes at gas mark 4/180C, and then for another 30 minutes at gas mark 2/150C. Test the lasagne with a knife. If the pasta is soft, you could scatter parmesan on top and brown the dish under a grill.