Whisk together the sugar, sambal, vinegar, soy sauce and water in a small sauce pan. Bring the sauce to a simmer and continue to simmer for 5 minutes. Add a couple tablespoons of water to the cornstarch and mix well. Whisk the cornstarch slurry into the simmering sauce and continue to simmer for about another 5 minutes. The sauce will be reduced and thick and will continue to thicken as it cools.