This is one of the many vegetables I was introduced to when I first came to Germany in the early 1970s.
The standard way of cooking it in those days as practised by my mother in law was to chop it into cubes and boil the living daylights out of it and serve it in an insipid white sauce. Fortunately that has changed and there are some lovely recipes out there now which let the kohlrabi speak for itself and retain its flavour.
Actually I love them and would grow them in the garden if I had room.
They are delicious when absolutely fresh and can be eaten raw. I always put a plate of veggies out for the grandchildren whilst I'm cooking. This can include cucumber and strips of peppers and carrot but also sticks of kohlrabi. If I haven't nibbled it all myself.
It can be grated - raw - into a salad - on its own or mixed with carrots.
To cook it, chop it into sticks or cubes. It doesn't take long to cook - about as long as a carrot. If they are still fresh, you can also chop the leaves and add these for the last few minutes of cooking time.
Sliced very thinly, I can imagine they would also go well in a stir fry.
I don't know how yours were still hard after 30 mins. They must have been very old.
You need to serve another vegetable with it if you are doing meat and 2 veg because the flesh is white and brings no colour to the plate.
My mother always paid a lot of attention to colour after realising that she'd served an all white menu of fish, cauliflower and mashed potatoes once early in her marriage when her brother and his wife came to visit.
