OK I cooked up the kohl rabi last night, I picked the other one that I thought was ready so there would be enough. It was a little green and crunchy and I had my reservations about using it but I thought it would be a shame to throw it out without trying it. The first one I picked was nice and white.
Anyway I peeled them both as I thought the skin would be a bit tough. Then I chopped and boiled the bulbs until tender, fried an onion in olive oil added some garlic and then the washed and chopped kohl rabi leaves. These were sauteed (lid on) for a few minutes until wilted, then I added a little cream and pureed the whole lot (including the bulbs of course).
Anyway, the verdict was.... not bad but not delicious. However, I wonder if my kohl rabi was a bit old and tough and that this recipe would be nicer with smaller, younger plants. Or maybe I stuffed up by putting in the greener one. In any case, I have put some more seedlings in the garden so I'll try again in a while. Maybe I'll another recipe also.