Cook peanut butter with sambal oelek or sambal manis, ketjap manis, and coconut milk.
Simmer until it has the consistency of mayonnaise. If the sauce breaks, add drops of water and whisk vigorously till it comes back together. Season to taste with more sambal or ketjap. Finally, add a dash of lime juice.
Serve sauce over potato fries. Top with a drizzle of mayo and chopped onions.