For the filling:
Place the potatoes in a pot and add enough water to cover. Boil over medium-high heat until the potatoes are cooked through and tender, about 15 minutes. Drain the potatoes and let them cool, then coarsely chop into bite-size pieces.
Put the oil and ghee in a wok or large frying pan over medium heat. When the oil is hot and shimmering, add one black mustard seed. When the seed sizzles and pops, add the rest of the mustard seeds and asafetida. Keep a lid handy to cover the pan while the mustard seeds are popping. When the popping starts to subside (a few seconds), immediately rub the curry leaves between your fingers a little to release their natural oils, and drop them, the ginger, and green chile into the oil. Cover immediately, as moisture from the curry leaves will cause the oil to spatter. Then stir to evenly coat everything with oil and continue to fry until the ginger and chile are less raw, 10 to 15 seconds. Add the onion and turmeric powder to the pan. Turn the heat to medium. Mix well and cook until the onions is softened and translucent. Mix in the potato and stir-fry until they start to become soft and mashable. If the pan is getting dry, add a little oil. Turn off the heat. Mix in the lemon juice and cilantro. Taste for lemon juice and salt and adjust if needed before serving.
For the chutney:
Place dried coconut in a little hot water to plump up. In a blender or food processor, add in ginger, serrano chili, red onion and coconut. Grind, adding as little water as possible to get blades moving. Next add in chopped cilantro, lemon juice, and salt to taste. Continue to add water as needed. Keep blending and scraping down the sides. The chutney is done when it reaches a creamy paste-like consistency but still has some texture from the coconut. If you want a thinner consistency, add water accordingly. At a low speed, add yogurt and more salt to taste. Transfer chutney to a bowl. For an extra flavorful chutney, add in ½ tsp mustard seeds, a pinch of asafoetida, and 3 curry leaves, prepared according to the directions above.
The chutney is best served fresh, but will last a few days in the refrigerator. If you refrigerate the chutney, it will thicken up so for re-serving just mix in little water or lemon juice to loosen it up.
Wash the butter lettuce leaves and pat them dry with a paper towel. Fill each lettuce leaf with 2 tablespoons of potato curry and 1 teaspoon of chutney. Eat as you would a lettuce wrap.