Kalettes are a cross between Brussels sprouts and kale, they were created using natural crossing techniques, no GM involved. Just like sprouts they grow on the stem of the plant and also like sprouts the leaves of the mature plant are also lovely, as is the kalette top.
First please forget everything you know about kalettes from your supermarket experience, or most gardening books and seed suppliers! Kalettes are so much better than they would have you believe!
I use a rating system to help me decide what to grow and it considers lots of factors, but the main ones are: how tasty it is, how healthy it is to eat, how expensive it is to buy, how big its harvest is, when its harvest period is and whether I can buy it organically and if not how much pesticide commercial growers use.
Kalettes win out on almost every category and they come top overall, when everything's considered:
Kalettes or Flower Sprouts as they are sometimes called
Kalettes are best sown in early/mid of March, although you can do a second sowing in early April for a later, but slightly smaller harvest. Just like Brussel Sprouts it's important to grow big plants, so give them plenty of time!
We like the seeds supplied by Johnson's in the UK. These packets contain multiple varieties that give a successional harvest, which is extremely useful. The seeds are expensive, but well worth it.
I sow Kalettes the same as all other brassicas. I fill pot with compost, level the surface, sprinkle a couple of dozen seeds on it and cover with 1cm of compost. I germinate them in the house, but not in a warm place, about 18c is ideal. They will germinate after about a week.
For more details on how I sow seeds and all of the products I use, see my guide to sowing.