Bring 375 ml water and cream to the boil. In the meantime peel kohlrabis, halve it and cut it into slices. Season cream mixture with salt. Covered kohlrabi and cook for 10-12 minutes. In the meantime cut ham into strips. Wash basil, shake dry, remove leaves. Put something aside for garnishing.
Bind the cream mixture with sauce thickener, bring to the boil. Season to taste with salt and pepper. Stir in basil and ham. Pour into a casserole dish and sprinkle with cheese. Gratinate under a hot grill or in a preheated oven (electric cooker: 225 °C/ convection oven: 200 °C/ gas: level 4) for 5-7 minutes. Garnish with basil