Coarsely blend or process peanuts or alternatively use a mortar and pestle.

Heat 2 tablespoons (30ml) oil in a medium skillet over medium-high heat until shimmering. Add remaining 1/3 of spice paste and cook, stirring, until fragrant, about 1 minute. 

If using pulp, soak and strain tamarind pulp by combining 2 tablespoons pulp with 2 tablespoons warm water and massage with your fingertips until softened. Press through a fine-mesh strainer. Keep the juice and discard the remaining pulp.

Add  peanuts, tamarind juice, remaining oil, kecap manis or fish sauce, and 1/2 cup water. Stir to combine. Once liquid comes to a simmer and turns creamy, adjust consistency with rice wine vinegar and more water as necessary to produce a creamy sauce that just barely flows. Season to taste with a little sugar if desired. Leftover sauce can be stored for several weeks in a covered container in the refrigerator.