Soak the dried chilli in hot water for about 20 mins or until they have softened. Wash and squeeze out the excess water.
Place the Assam/tamarind in a bowl. Add 1 cup of water to the tamarind and use your hand to squeeze the tamarind until the seeds come out.
Pour the tamarind over a sieve and using your hand to extract the juices from the tamarind to get tamarind water.
Put the shallots, chilli, dried chilli, garlic and 1 tsp of oil into a blender. Blend them finely.
In a non stick pan, heat up 3 TBsp of oil over medium low heat.
Pour the blended mixture to the pan and saute for about 5-6 mins, Turn the heat to low.
When it is aromatic, add in tamarind juice, 1/2 tsp salt and 3 TBsp sugar and fry until a layer of chilli oil surfaces (about 2-3 mins). More water can be added if it is too dry. More sugar can be added according to taste.
Serve the chilli sauce with Mee Siam.
Buy the Tamarind from Thailand as some like those from Malaysia and Indonesia tend to be very salty.
Add more tamarind and sugar if you prefer a more sourish and sweeter taste.
Control the fire well when frying chilli paste as the paste gets burnt easily. It's safer to use low heat even it slows down the cooking time.
Add some chilli padi if you prefer it to be more spicy.