Preheat the oven to 180 C. Remove the outer ends of the chicory and remove any ugly looking leaves. Than cut the chicory lengthwise in four pieces. Pour the oliveoil into an ovendish and put the chicory in, single layer, cut side up.
Pour the wine or stock in and cover with aluminium foil. Put in the oven for ten minutes while you prepare the rest of the ingredients.
Cut the chicken into 1 cm thick strips. Add salt and pepper and melt the butter in a large frying pan until hot. Ad the chicken and bake until golden brown. Add the onion and garlic and bake this for another minute.
Remove the ovendish from the oven and add the chicken mixture to the chicory. Put the foil back and set to the side while you're preparing the sauce.
Melt the butter for the sauce in the frying pan (no need to wash first) and stir in the flour. Add the milk bit by bit and keep stirring until the mixture thickens a bit
Remove from the fire and add the creme fraiche, the sage and the mustard. Stir and taste if you need to ad any more seasoning or mustard.
Pour the sauce over the chicory and chicken and cover with grated cheese. Put this in the oven - without the foil this time - for about 25-30 minutes until the sauce bubbles and the cheese is golden