I cooked my first kohlrabi from the garden for my lunch yesterday, the way I had it when I was a child and which is still my favorite way to eat it (apart from raw). It turned out very good, nice and soft. Here is what I did.
Peel kohlrabi, cut away all the woody bits around the stem and where the leaves were. Then cut into small cubes and cook in salt water together with some peas until tender. Make a light roux with some butter and flour, use some of the cooking water to make a sauce. When the sauce is as thick as you like it, add the cooked vegetables. That's all. You can also omit the sauce part and just serve it with some butter or mashed.