Turn on the oven at 200°C. Peel the pumpkin, cut it into slices of about 2 cm thick, and put it on a baking sheet.
Add the leek, washed and sliced, the extra virgin olive oil, sage, a little salt, and pepper, and mix with your hands.
Roast for 10 minutes in the preheated oven, then add the cleaned and sliced mushrooms. Roast for another 10 minutes, then remove the vegetables from the oven and lower the temperature to 180°C.
Take the shortcrust pastry from the fridge and use it to coat one rectangular baking tray of 30 x 20 cm (or a round one of 26 cm in diameter), cutting away the dough that comes out from the edges with a sharp knife. Prick the bottom with a fork and put it in the freezer for 5 minutes.
Cover the cold pastry with a sheet of parchment paper, add the baking weights, and blind bake the dough for 15 minutes. Remove the weights and paper and continue baking for another 15 minutes, then take the base out of the oven, keeping the oven on.
While the base is baking, prepare the filling or the liquid part of the quiche. Beat the whole egg and the yolks in a bowl, add the cream and milk, salt, a pinch of black pepper, and a little nutmeg. Mix well and keep aside.
Cut the cheese into small cubes.
Arrange the roasted vegetables on top of the base of the quiche, add the cheese cubes and finally, pour the liquid mixture. Be careful because, based on the shape and depth of the tray, you may not need all the liquid.Put the quiche in the oven and bake for 25 - 35 minutes, or until the liquid part becomes solid and the edges of the quiche are golden brown. Serve it while warm.