Cut the butter into small pieces and work it into the flour with your fingers. Add the cheese and salt and quickly gather the dough together. Press the dough into a greased springform pan (approx. 22 cm in diameter). The dough should reach halfway up the sides. Cover and refrigerate for at least 30 min. or overnight. Prick the crust and pre-bake in the middle of the oven for approx. 12 min. at 200°C (conventional oven).
Melt the butter in a saucepan. Add the curry and wait until it has stopped bubbling. Sauté the onions for about 1 min., then add the mushrooms and sauté until all the moisture is gone, approx. 6 min. Pour the filling into the pre-baked crust. Beat the eggs with the milk. Then add the rest of the ingredients. Pour the egg mixture over the vegetables and bake in the middle of the oven for approx. 40 min. at 200°C (conventional oven). Serve the warm tart with a green salad.