This simple rustic pie uses an oil-based pastry that is fast and easy to make. You can make a galette with different fruits or berries depending on the season and what you have on hand.
Mix flour, cornstarch, sugar, salt and baking soda in a mixing bowl until thoroughly blended.
With fork or pastry cutter, blend the vegetable and olive oils into the flour mixture until it is very crumbly and there are not traces of unmixed flour.
Mix water and vinegar together and pour over flour mixture while blending with a fork or spoon. Stir into a ball shape and place in the fridge while you make the filling.
Stir together rhubarb, apple, sugar, ginger, cardamom, orange zest (if using) and salt. Let the fruit sit for 15 minutes until it starts to release some of its liquid. While the fruit is resting, preheat the oven to 350 degrees F / 177 degrees C. Lightly grease a baking sheet or line with parchment.
Use a slotted spoon to remove the fruit and place it in a new bowl. Remove three tablespoons / 45 ml of the liquid at the bottom of the bowl. Mix these three tablespoons / 45 ml with the cornstarch and stir into the rhubarb.
Remove the pastry dough from the fridge and place on a lightly floured surface. Roll into a circle about 13 inches in diameter.
Place the pastry circle on the prepared baking sheet. Place the rhubarb in the center of the circle and spread to within 2 or 3 inches / 5-7.5 cm of the edge. Fold the edges over the filling, leaving some of the fruit visible in the center. Sprinkle with coarse sugar if using.
Bake for 40 minutes, or until the pastry is lightly browned. Remove from oven and let sit for at least 10 minutes before serving.
Pastry and filling can be made a day or two in advance and assembled when needed.
The baked galette can be made up to two days ahead and stored covered at room temperature or in the fridge.