In a skillet, add the olive oil, when hot, add the leeks and onions, add salt and pepper, sauté until translucent.
Add the cream cheese, stir to combine, add the remainder of the ingredients for the quiche, stir for 3 minutes more. Turn off the heat, reserve.
GLUTEN-FREE SHORCRUST PASTRY:
Add all the ingredients for the shortcrust pastry to a bowl, blend very well, or mash it with a fork. If you feel your crust is too wet, add a tablespoon of cornstarch, if you feel that your crust is too dry, add a tablespoon of the water you’ve used to cook the chickpeas or water.
ASSEMBLE THE QUICHE:
Using a 25cm (10 inches) pie dish with a removable bottom, spread the quiche shortcrust pastry even all over the bottom of the pie dish as well as the sides. Make all the surface and sides are even. Cut the excess pastry with a knife, pierce it all over (sides included) with a fork; put it in the preheated oven for 15-20 minutes at 200C (390F).
Remove the baked shortcrust pastry from the oven, allow it to cool, add the quiche filling, garnish with red onions, leeks, and fresh sage leaves, put it back in the oven at 185C (374F) for 20 minutes.
Remove from the oven, wait until the quiche has cooled a bit, remove from the baking tray, and serve it while still hot.