First place the cauliflower florets, onions and vinegar together in a large saucepan, add the nutmeg and allspice and bring to the boil.
Cover and simmer for 8 minutes. Now, take the lid off and stir in the cucumber, beans, sugar and garlic. Bring the mixture up to simmering point again and cook for a further 5 minutes uncovered. The vegetables should still all be slightly crisp – so don’t go away and forget them.
Now set a large colander over a large bowl and pour the contents of the saucepan into it and leave it all to drain (reserving the vinegar). Then mix the mustard powder, turmeric and corn flour together in a bowl. Gradually work in 2 additional tablespoons of vinegar and 1-2 tablespoons of water so that the mixture becomes a fairly loose paste. Next add a ladleful of the hot vinegar drained from the vegetables, and transfer the blend to the saucepan. Bring to the boil, whisking with a balloon whisk, and gradually adding the remaining hot vinegar. Boil gently for 5 minutes, then transfer the vegetables from the colander to the large bowl, and pour over the sauce. Stir well to mix, then spoon the piccalilli into warm sterilised jars (see below), with waxed discs and tight lids. Keep for 2 months in a cool, dark place before eating.