Slice the onion and carrot. Put them into a saucepan with the bacon and fry them in the fat without browning them for 10 min. Slice and add the tomatoes and cook them for 5 min. Sprinkle in the rice flour, add the stock or juice, stir till the sauce boils. Simmer the sauce for 45 min. Rub the sauce through a hair or nylon sieve. Reheat, season and add lemon juice, sugar and nutmeg to taste.