Sift the flour into a bowl with the mustard powder, celery salt, paprika and pepper to taste. Make a well in the centre, add the egg yolks and beat to mix thoroughly, gradually working the dry ingredients into the centre. Beat in enough beer to make a batter with a thick coating consistency.

Cover the bowl with cling film, then set aside in a cool place for 2 hours (see Time).

Grill the bacon until cooked but not crisp. Drain on absorbent paper, then cut into 2.5 cm (1 inch) lengths.

Heat a little oil in a frying-pan. Add the onion and pepper and fry gently for 5 minutes until the onion is soft and lightly coloured. Remove with a slotted spoon and add to the bacon.

Pour enough oil into a deep-fat frier to come halfway up the sides. Heat the oil gently to 190C/375F, or until a stale bread cube turns golden in 50 seconds.

Meanwhile, in a clean dry bowl, whisk the egg whites until they are standing in stiff peaks. Using a large metal spoon, carefully fold the egg whites into the batter with the bacon, onion and green pepper.

Drop a few tablespoonfuls of batter into the hot oil and deep-fry for 3-4 minutes, until puffed and golden brown. Drain well on absorbent paper and keep hot while frying the remainder, but remember to reheat the oil between each batch.

Serve with tomato wedges.