here's my say:
1) don't use wanton wrappers from oriental stores. use dow for the cover.
2) pork meat naturally has more fat than chicken, so go for pork, if you're really looking for a tasty momo.
3) put some butter on the ground pork while mixing it with salt and spice and let it stay for a night.
for achar:
1) use sesame seed, mustard and cumin seeds. take a cup of sesame, a tea-spoonful of mustard and tea-spoonful of cumin seeds. mix then and roast the mixture on a pan for 2-3 minutes in a dry frying pan.
2) roast 3-4 tomatoes in an oven for 15 minutes at 400 degrees.
3) grind the roasted seeds in a grinder with some water to make sure they mix properly. then peel off the tomatoes cover and put it in the mixture of crushed seeds and blend them for until everything mixes properly. add some water if the mixture is too thick.
4) add salt, cilantro, lemon juice according to your taste. put some ginger garlic paste and blend everything for a while.
that is it! :D :P