Slow-cooker vegetable lasagna

Lunch had to cook while we were out on our bike ride (from Timperley to town via the canal tow-path, a most scenic route and one which treated us to, among other things, the sight of two enormous white swans flying straight towards us down the canal just outside of Sale) and be ready for when we got in, tired and hungry and in need of sustenance.  I thought initially of making lasagna and reheating it, but then it occurred to me to wonder whether it was possible to do it in the slow cooker so it would be hot and waiting for us.  The internet said yes, and gave me the idea of using pesto and spinach as well.

I modified the recipe a fair bit, as I wanted more vegetables (the original called for just spinach and tomato pasta sauce), and a white sauce instead of ricotta.  It turned out pretty well but could have used a touch more salt, in my opinion; next time I'll taste and season the vegetable sauce rather than just piling it all in and trusting to Dolmio!  I also have no idea what quantity of lasagna noodles were required as I was using up various tag ends of boxes from the pantry and didn't keep count, but probably about 1-1.5 boxes would be plenty.

Lasagna noodles, some (see above)
200g packet spinach (that was how big they were at the shop; I could have used more)
about 1/2 small jar pesto
1.5 cups grated cheese
1/4 cup red wine
1/4 cup hot water

At some point while the sauces are cooking, put the slow cooker on to preheat (if required by instructions).

Vegetable sauce
large onion, chopped
2 cloves garlic, finely chopped
2 medium carrots, chopped
1-2 stalks celery, chopped
1/2 red pepper and 1/2 yellow pepper (one guest didn't like green pepper), chopped
200g mushrooms, sliced (cut in half first if large)
2 x 300g jars tomato pasta sauce (this is totally cheating and you can of course use canned tomatoes and add extra herbs and seasoning!)
1/4 cup red wine
salt and freshly ground black pepper

Heat a small amount of oil in a large pan and fry onion, garlic, carrots, celery and pepper (adding each to pan as it is chopped); add mushrooms and pasta sauce; rinse jars with red wine and add to pan.  Simmer until vegetables are cooked; season to taste.

White sauce
30g butter
1 heaped tbs plain flour
500ml milk
salt and pepper

Melt butter over medium heat, stir in flour, cook for a couple of minutes.  Remove from heat, add milk gradually, whisking to incorporate until a smooth mixture is formed.  Return to heat and cook, whisking constantly, until thickened and just at a boil; allow to cook a couple more minutes.  Season with salt and pepper.

To assemble:
Put a thin layer of vegetable sauce in the base of the slow cooker; spread pesto over lasagna sheets and use to cover sauce.  Layer vegetable sauce, spinach, white sauce and more pesto-spread lasagna sheets; vegetable sauce, spinach, half the cheese and lasagna sheets; vegetable sauce, spinach and lasagna; and vegetable sauce, white sauce and remaining cheese.  Or, you know, whatever combination suits the amounts of ingredients you have...

Rinse out vegetable sauce pan with remaining wine and water, pour over everything in the slow cooker.  Shut the lid and cook on high for about 3-4 hours.  Ours was perfect at 3:30, having gone in at 11:30, and would probably have been fine sooner -- but would also probably have benefited from being removed from the heat and let stand for a little while to firm up.  Even so, it was heartily satisfying, rich and tasty without any hard dry bits, but with a decent browned crust.  Leftovers tasted even better the next day!

Preparation time: about an hour to make sauces and assemble, plus 3-4 hours slow cooker time
Makes: Enough for four hungry people post-bike ride, plus enough left over to freeze a box and have three small meals the next day -- probably serves 6-8, the former very generously, the latter quite adequately.