1. To make the bases, mix the flour, yoghurt, olive oil and salt together in a bowl to combine. On a well floured bench, knead the dough until soft and elastic, adding more flour if needed. Divide dough into two and roll each out to desired pizza shape and thickness. Place onto trays or pizza stones.
2. Mix garlic and duck fat together in a bowl and using a pastry brush, paint onto the base of each pizza. Top with the sliced potato, season with salt and pepper and sprinkle with thyme and rosemary.
3. Remove duck legs from the pack and thinly slice while chilled. Discard bones.
4. Add sliced duck onto each pizza. Spoon on onion jam or onion relish. Tear fresh mozzarella and place evenly onto each pizza.
5. Cook in the oven for 8-10 minutes or until the base has browned and cooked through.