1 grapefruit
1 orange
1 lime
1/4 C sugar
1/4 C soy sauce
1/4 C rice vinegar

Use a zester to remove the colorful outer rind from the citrus fruits and save it. Juice the fruits and combine the juices.
Put the sugar in a dry pan over medium-high heat and swirl the pan until the sugar has begun to dissolve; it will be caramel-colored. Carefully pour in the fruit juice (mixture will boil and steam rapidly before settling into a steady boil. Boil about 2 minutes, swirling the pan now and again.
When all the carmelized sugar has dissolved, add the soy sauce and vinegar. Drop in half the citrus zest and continue boiling 2 or 3 minutes, until slightly thickened. Zest may be left in or strained out.
Serve the sauce warm or at room temperature with seafood such as pan-seared salmon or scallops. Sprinkle extra zest over the seafood