Combine all the ingredients except the ketchup in a small saucepan, bring to a simmer and cook for 5-6 minutes until thickened.
Add ketchup and adjust seasoning to liking.
Chole / Cholay for Samosa Chaat
Combine all the chole/cholay ingredients except chaat masala in a small saucepan, bring to a boil, simmer till the chickpeas are tender, approximately 10 minutes.
Mash a little to create a thicker 'gravy', you want some liquid left in there because it really adds to the overall dish.
Add chaat masala, and adjust seasoning.
Sweet Yoghurt
Whisk together yoghurt, sugar, and cold water
Assembly
For each samosa chaat plate break up one heated samosa, ladle over a big spoon of the cholay mixture, drizzle over ¼-1/3 cup of your sweet yoghurt, then put about 2-3 tbsp each of imli ki chutney and red chutney, top with papri and chaat masala and a little cilantro.
Notes
I used bhunna zeera and dhania for extra flavour, but if you don't have it then regular is fine, it'll just be a little less smoky
how much yoghurt you want overtop will depend a little on you, but this quantity should give you room to adjust
for potato samoasa I use the bigger kind with the crispy, flaky outer later, but if you are using the more petite variety you can use twice the number of samosas. For samosa chaat cups refer to the post.