Bring spinach to the boil in a small pot and defrost over low heat for about 5 minutes. Preheat oven (electric cooker: 200 °C/circulating air: 175 °C/gas: see manufacturer). Peel and chop onion. Heat 1 tablespoon of oil in a pot.
Fry the onion in it. Add tomatoes, bring to the boil and simmer for about 5 minutes. Season with salt, pepper and sugar.
Beat the eggs. Wash the meat, dab dry and cut lengthwise, season with salt and pepper. Mix ricotta, spinach and parmesan, season with salt and pepper. Fill into the chicken fillets and fold up.
Turn fillets first in egg, then in breadcrumbs. Heat 4 tablespoons of oil in a frying pan. Fry the fillets for about 4 minutes until golden brown.
Place in an ovenproof dish and pour the tomato sauce over it. Add the sour cream in splodges. Bake in a hot oven for 10-15 minutes.
Wash the basil, shake dry and pluck the leaves. Remove the casserole dish from the oven, sprinkle with basil and serve. Ciabatta is delicious with it.