Let’s make the peanut sauce first, by blending everything except tamarind paste, soft shrimp paste, and sweet soy sauce, in a food processor, until smooth texture. Pour mixture onto a pan, then add in tamarind and petis, stir to combine well, cook until bubbly, adding more water as needed, and sweetened slightly with sweet soy sauce (some like it sweeter, some like it spicy, so adjust to your liking)