we start preparing the shortcrust pastry. Make a volcano with the flour and add a pinch of salt and the butter (which must be very cold) cut into cubes. We work with the fingertips until no pieces of butter are noticeable.
We make a hole in the center and add the egg white, from which we will have separated a tablespoon. Mix until you get a homogeneous mass, without going overboard with the kneading so that we do not have a hard dough. Wrap the dough in plastic wrap and let it rest for 30 minutes in the fridge.
While this happens, we prepare the filling. For it Chop the vegetables and poach them in a frying pan with a little oil, over low heat, starting with the spring onion. When it has become slightly transparent, add the carrot and, ten minutes later, the zucchini. Sauté five more minutes and remove.
Mix the eggs with the liquid cream and we salt and pepper without going over and taking into account the amount of cheese in the quiche. Remove the dough from the fridge and spread it out with a rolling pin. We cover the base and sides of an 18 cm mold with it, remove the excess, prick the base and bake (covered with parchment paper and dry legumes that act as weight) for 20 minutes at 180ºC.
After this time, we take the base out of the oven and remove the legumes. Immediately brush it with the egg white that we have reserved, which it will curdle due to the effect of heat and will waterproof the dough (avoiding softening with the filling). Fill with vegetables, cheese and egg mixture. Bake again at 180ºC for 30 minutes or until golden brown. Let rest 10-15 minutes before serving.