Cook the lasagna noodles according to the package directions. Drain and keep them from sticking.
Cottage cheese layer: Mix cottage cheese, egg and ½ tsp onion salt for each pan.
Potato layer: Mix mashed potatoes with cheddar, salt, onion salt and pepper.
Prepare the onions: Melt the butter and sauté the chopped onions until softened and lightly golden.
In each of 4 greased 9×13 pan, layer: 5 noodles, Cottage cheese mixture, 5 noodles, Mashed potato/cheese mixture, 5 noodles, Buttered onions, spreading the butter over the top.
Cover tightly with foil.
Bake at 350°F for about 30 minutes.
Remove the foil and bake another 5–10 minutes to lightly brown the top.
Let stand 10 minutes before cutting.
Cut each pan into 12 portions.