Wash and peel the kohlrabi and carrots. Cut the kohlrabi into pieces and the carrots into thin slices.
Wash and shake dry the rosemary. Peel and dice the onion.
Heat the rapeseed oil in a pan and saute the onion over a medium heat until softened. Add the kohlrabi and carrots and fry for another 2 minutes.
Add the allspice, rosemary and stock. Simmer over a medium heat for 10-12 minutes. Remove from the heat and cool slightly.
Meanwhile, mix together the quark, eggs, milk, salt, pepper and herbs.
Fold the kohlrabi and carrots into the quark mixture. Pour into an ovenproof dish and bake in a preheated oven at 180°C (160°C fan, gas 4).
Meanwhile, toast the sunflower seeds in a dry non-stick pan until golden brown. Scatter over the casserole and serve.