Potato onions or Allium cepa var. aggregatum are an easy to grow relative of the Shallot & not related to the Potato at all.
Potato Onions produce a cluster of 10 to 15 bulbs from each bulb. they're generally larger than those of the Shallot and will store for a much longer period than any other Onion.
Potato onions can be planted any time from March until early September in a position with at least 6 hours of Summer Sun in well prepared beds that have been liberally dosed with a mixture of garden lime & dolomite lime & a light application of Super Phosphate to promote healthy root & bulb production (they prefer a pH of 6.5 - 7.5)
Water regularly but don’t over water as the bulbs can dampen off if the area is kept to moist.
Bulbs take about 6 months to mature. The green leaves of the Potato Onion can be harvested & used as a substitute for Spring Onions & in late summer as the foliage begins to yellow & die off the bulbs can be carefully lifted & left in a sunny & dry position for a week to allow the outer skins to firm up ready for storage for the months ahead. Store your Potato Onions somewhere dry and airy to cure - this takes about two months, though once initial drying is done they can be eaten. Bulbs store for about nine months.
Potato onions can be used as you would a Shallot in many dishes where you would like a mild onion flavour. The best idea is to eat the larger bulbs and replant the smaller ones so you have a continuous supply.