Peel the kohlrabi and cut into sticks. Cut broccoli into small florets. Clean and wash spring onions and cut into wide rings. Cook kohlrabi in salted water for about 4 minutes. Add broccoli after about 1 minute.
Drain the vegetables.
Take the puff pastry out of the fridge about 10 minutes before processing. Wash the meat, dab dry and cut into cubes. Heat oil in a coated pan. Fry the meat for 3-4 minutes until golden brown.
Add kohlrabi, broccoli and spring onions and deglaze with cream. Season to taste with salt, pepper and nutmeg and simmer again for about 5 minutes.
Put the ragout in an ovenproof dish. Cut out the puff pastry about 2 cm larger than the form. Cut out small moons from the remaining dough and decorate the dough cover with them. Place the dough cover on the baking dish and press down on the edges.
Mix the egg yolk and milk and brush the puff pastry with it. Bake the casserole in a preheated oven (electric cooker: 200 °C/ convection oven: 175 °C/ gas: see manufacturer) for approx. 25 minutes until golden brown. Cover the surface with aluminium foil if necessary.