Boil the noodles in salted water until just tender and drain. Fry the onion in 3 tablespoons of fat or oil until soft. Cool a little, then mix with the eggs and noodles. Add a little salt. Line a loaf pan or mould with greaseproof paper or foil and grease well with the remaining fat. Pour in the noodle and egg mixture and bake in a preheated 350°F/180°C/gas 4 oven for about 45–60 minutes, or until firm and lightly brown on top. Turn out, peel off the foil, and serve hot cut in slices.