"I added the following:

The zest of 1/2 lime
1 tsp Cumin
Sugar to taste
Hot red pepper flakes to taste

In addition, I used red curry paste instead of powder. I like the depth of flavor the paste gives as opposed to the powder. I also thickened it just a bit with a cornstarch slurry, but AFTER the shrimp were cooked.

A note on the cooking time, I let the sauce simmer for about 1/2 hour to let the flavors really blend. The sauce is really a "taste as you go" kind of thing because it's so specific to what each person likes. The shrimp DO NOT take 12-15 minutes to cook. I let mine cook for about 5 minutes. They were done perfectly and I used jumbo shrimp (because they looked the best that day at the market) and 5 minutes was all it took. You don't even have to have the heat on to cook the shrimp. They will cook from the heat of the sauce alone.

I also garnished with a little fresh basil chiffonade and served over Jasmine rice."