Make the tomato sauce: sauté the onion in a little oil, add the canned tomatoes, bring to the boil with the spices, simmer until a little thickened. Possibly puree. Season the spinach. Layer in the baking dish in the following order: tomato sauce at the bottom, then alternately lasagne sheets, spinach, sour cream and feta (twice). Finally, lasagne sheets, tomato sauce and Emmental cheese. Bake in a preheated electric oven at 200 ° C for about 30 minutes.