Kohlrabi is in the brassica family and is related to kale, broccoli and cabbage.
Often referred to as the "German turnip," it is actually the stem, not the root, that is eaten. Think of a bulbous broccoli stem!
It should be peeled before use. Sometimes they have red skin but both green and red varieties have the same white flesh inside.
You can use kohlrabi as you would a turnip or cabbage. It's delicious sliced into thin wedges and sprinkled with salt or grated into salads.
The kossak variety that we grow is meant to be that big! I've seen some bigger than my head at a farmers market in VT.
Kohlrabi goes well with butter, sour cream, dill, mustard and horseradish.
Store like greens, in a plastic bag in the refrigerator.
RECIPES
Kohlrabi with Horseradish:
about 1 pound peeled kohlrabi
2 to 4 tablespoons creme fraiche or sour cream
prepared horseradish in vinegar
2 teaspoons of chopped dill
salt and pepper
Slice the kohlrabi into julienne strips or wedges. Steam until tender, 5 to 8 minutes, then remove to a bowl and toss with creme fraiche, horseradish and dill. Season with salt and pepper to taste. (Vegetarian Cooking for Everyone by Deborah Madison, p384)