For the tamarind yoghurt
Place the chana dal in a pressure cooker along with a teaspoon of salt and a cup of water and cook on high for 12 minutes. Rinse well and set aside.
Meanwhile, grate the potato and refrigerate until needed.
Heat a large pan with 1 tsp oil and sauté the spices and dal for 2-3 minutes. Transfer to a food processor and pulse until smooth. Stir in the chopped coriander.
Add the cornflour and salt to the grated potato; mix to combine to form a non-sticky dough.
To shape the aloo tikki, take a small portion of the potato mixture in between your palms. Roll it and gently flatten it with your fingers. If the potato mixture seems sticky, moisten your fingers with a teaspoon of oil.
Make a well in the centre of the potato ball, fill in a teaspoon of dal stuffing. Close the edges. Gently flatten the balls once again to get the thickness of an inch or so. Similarly, shape all the patties.
Heat the oil in a frying pan over a medium heat and shallow fry the aloo tikkis in small batches over a low-medium heat. Drain on paper towels.
To make the yoghurt, combine all the ingredients. Serve with the aloo tikkis.