Preheat your oven to 180 degrees Celsius (355 degrees Fahrenheit) In a bowl combine the flour, olive oil, salt and water and combine until it forms a nice dough soft and create a ball with your hands.
Sprinkle some flour on your bench top and roll the dough in a circle then place the dough in a tart tin (greased with olive oil or lined with baking paper to make it easier to remove) (or flatten your dough in between 2 sheets of parchment paper).
Place in the oven to blind bake for 10 minutes (using dry beans for example)
Meanwhile, slice your onions finely (or using a mandolin). Cook them in a pan with olive oil until soft. Then add the sugar and balsamic vinegar. Stir often and cook until soft and caramelised.
Next to the onions, cook the sliced mushrooms in a pan with olive oil until cooked. Then leave to the side.
In a blender, combine the silken tofu, nutritional yeast, salt, pepper, mustard and arrowroot flour and blend until well combined.
Then assemble the quiche. Layering the onions first then pouring the silken tofu filling and topping with the cooked mushrooms. Sprinkle some rosemary on top and place the quiche to bake in the oven.
Bake at 180 degrees Celsius/ 355 degrees Fahrenheit for 30-40 minutes or until golden. Leave to cool then serve with a salad.
