Wash the crab apples and cut them in quarters, removing any damaged parts but leaving on the skin and cores. Put into a large enamel pan, cover with cold water and boil gently until reduced to a pulp. Strain pulp through a muslin bag.
Meanwhile, thinly slice the peel from three or four sweet oranges. Simmer this gently in enough water barely to cover it, for about ½ hour. Add this to the strained juice from the crab apples. The proportions should be, roughly, two pints crab apple juice to one pint orange peel and water.
Bring the crab apple juice and orange peel water to the boil and to three pints of the mixture add 3 lbs sugar, and boil gently until it sets when tested on a plate (about 20 minutes). Put into warmed jars and cover as soon as it is cold. If no orange peel is available the crab apple jelly is delicious by itself.