Easy Vegan Mushroom Pie

large portobello mushrooms (, see recipe notes for tips on choosing th e perfect mushroom shape)

oil of choice (, OPTIONAL - use water or broth to saute the onions if you prefer)

medium onion (, cut in half then sliced into very thin half moons)

sugar (, optional )

dried thyme

/ 1 cup all purpose flour (, measure the flour by spooning into the cup and levelling with the back of a knife. Do not scoop. If in the UK use plain flour. )

salt (, finely ground)

/ ¼ cup + 2 tablespoons vegan butter (, hard and cold)

few tablespoons ice cold water

milk of choice

maple syrup (, or other liquid sweetener)