1/2 C Sugar
1 small red onion
3/4C sour cream
2T horseradish (finely grated if using fresh)
2T wasabi, bloomed if using fresh
Put cranberries, onion, sour cream, and half of the sugar in a food processor and process until smooth. Then add small amounts of the horseradish, wasabi, and sugar until you achieve desired balance of heat, tang, and sweet. Add salt and pepper to taste at end. Make a day ahead and refrigerate. Remove from refrigerator about 20 minutes before serving.
A note on the roots: The reason I add these in small amounts is because fresh versions can have unpredictable heat. I have yet to get both wasabi and horseradish fresh, but using powdered wasabi (re-hydrated to a paste) and jarred horseradish still produces an excellent sauce. This is particularly good on next day sandwiches.