First, prepare the filling: combine all the filling ingredients in a bowl. Roast them in a preheated oven at 200 °C for 20 to 25 minutes, making sure to stir the vegetables halfway through to ensure they roast evenly and get some color.
While the filling roasts, start on the dough. In a large bowl, rub the all-purpose flour with salt and your chosen fat (olive oil, ghee, or butter) until the mixture resembles coarse breadcrumbs. Stir in the cumin and crushed cashews.
Gradually sprinkle in the icy water, a little at a time, kneading the mixture until it forms a tight, cohesive dough. Don't add all the water at once; you want to achieve a firm but pliable texture. Set the dough aside to rest for 15 minutes.
Once rested, divide the dough into four sections and roll each into a ball. Lightly flour your work surface and use a rolling pin to flatten each ball into a thick disk. Lightly grease a muffin tray; if you have any empty cases, you can fill them with a little water to help with even baking.
Carefully place each of the four dough disks into the prepared muffin cases. Spoon a generous amount of the roasted vegetable filling into each tart, then gently pinch the edges of the dough around the filling to create a rustic border.
