In a large saucepan brown the onion, add the curry powder and cook for 1 minute.
Add all the other ingredients, bring to the boil, reduce heat and simmer until thick. Set aside.
To make the cheese sauce
Melt 40g butter in a large saucepan and slowly stir in 3 tablespoons plain flour.
Keep stirring and slowly add in 3 cups of milk.
Then add 1/2 cup of grated cheese and keep stirring until thick.
Grease the slow cooker bowl.
This makes sure the lasagna comes out easily and gives it a nice brown crust along the sides!
Add 1/2 of the tomato sauce into the bottom of the bowl, then add a layer of lasagna sheets,
breaking a sheet into pieces to fit the edges
Cover with half of the white sauce.
Then add the rest of the tomato sauce, a layer of lasagna sheets and the rest of the white sauce.
Top with the rest of the grated cheese and put a Tea Towel under the lid so the steam doesn't drip onto the cheese layer
Cook with the slow cooker on high for 2 hours