for kohlrabi, the way i've always done it is this: peel and cut into fairly thin slices, roughly 1/4 inch thick. if you have about 2-3 softball sized ones, put about a teaspoon of oil in a pot, heat on medum, add about 1/2 tsp each of black mustard seeds and cumin seeds. wait till seeds pop. add 1/4-1/2tsp turmeric powder to oil (depending on taste) and then add kohlrabi pieces. stir, add salt to taste, and cook till kohlrabi is done--it should be slighty translucent and soft, not at all crunchy. if you'd like you can add a jalapeno or serrano pepper while it's cooking too.
I'm sorry that this isnt a proper recipe, it's one of those things i've done so long i've gotten to the point where i never measure anything.
I hope you like it!

Marcella Hazan has a soup recipe. She says the Italian word is a blend of "cabbage" and "turnip" because that's basically what kohlrabi is and it can be treated as such. I'm presuming a gratin would be decent, too.

I've found it's good in slaw and during the most virtuous of my weight-loss days, I've snacked on big, crisp wedges since it's quite filling. Stir-fry. Grated in chicken or tuna salad.

I will never forget something Elizabeth Schneider wrote about kohlrabi since I consulted her book on exotic vegetables eagerly after finally bringing a bunch home for the first time: we always tend to have high expectations for produce we've never tried before. Implicit was the idea that you shouldn't expect it to knock your socks off any more than a stalk of celery might.

Wow! Thanks for the insight. What I gathered was that once cooked, kohlrabi can have a bit of an artichoke flavor, and raw-it is like cabbage and radish/turnip.
I wanted to use up some sprouting spuds so I made Kohlrabi Potato Soup in the same way I made potato leek soup. Here's a pic of the soup garnished with sauteed chiffonade of tat soi and chopped egg.