Serve this sauce with Chicken or Pork Satay.
In a medium skillet, heat oil over medium heat. Add onion and garlic, and cook until translucent, 3 to 5 minutes. Transfer to a blender. To the same skillet, add the chile paste and curry powder. Cook, stirring until fragrant, about 1 minute. Add to blender. Add the peanut butter, coconut milk, sugar, vinegar, salt, 2 tablespoons warm water, and 2 tablespoons of peanuts. Blend until smooth.
Transfer to a bowl, and let stand until room temperature. Before serving sprinkle with remaining peanuts. The sauce may be made 1 day ahead and refrigerated in an airtight container (press plastic wrap directly on top of the sauce to prevent a skin from forming.) Let sauce return room temperature for 1 hour before serving.