Thai-inspired Yam Curry

I think Yam is sometimes confused with Sweet Potato here - at least at the grocery store, the yam they sell tastes just like sweet potato.

The yam I remember from my younger days in India was a lot different - more roundish (not elongated), yellowish inside (not orange), neutral flavored (not sweet), with tough brown skin (not thin pinkish skin).

In any case, this yam recipe is inspired by thai flavors.

Ingredients
1 yam, cut into chunks
1 bunch spring onions, cut into 4" long pieces
1 bunch baby bok choy, cleaned, roughly chopped
2 tbsp oil
salt to taste
for sauce:
2-3 Tbsp tamarind concentrate or, fresh tamarind
1 medium shallot
1/2 stalk lemon grass
4-6 fresh chilies (i used red balloon chilies from my garden)
2" piece of ginger
1 Tbsp brown sugar (optional if yam is sweet)

Preparation:

1. if using fresh tamarind, shell it, soak it in hot water and extract pulp (remove the seeds) to get approximately 8 Tbsp; combine the sauce ingredients and blend it to a smooth paste
2. heat oil in a pan, add the yam chunks, some salt, some water and cook till half-done
3. then add the sauce, bok choy and some more water, cover and cook till yam is cooked through but not mushy
4. add the spring onions, stir well, adjust salt to taste and cook for a few minutes till spring onions soften
5. serve warm with steamed rice