Prepare the quiche dough by mixing flour, butter (previously soften in the microwave), egg, milk and salt until a smooth dough forms. Wrap and chill in the refrigerator for about 30 minutes.
Lightly sauté asparagus, mushrooms, onion and leek in a pan until slightly softened and fragrant. Add the crumbled tofu toward the end of the sautéing so it warms and absorbs flavor. Stir in the spinach just before removing from the heat and let it wilt gently.
In a separate bowl, whisk together the eggs, sour cream, nutmeg, salt and pepper.
Roll out the dough and line a greased 28 cm quiche dish. Add the vegetable-tofu mixture and pour the egg mixture evenly over the filling.
Bake at 200°C (top/bottom heat) for about 30–40 minutes until the quiche is golden and set.
Let the quiche rest for 10 minutes before slicing.