When grilling your hamburgers, add white wine diluted with water, cover with a lid, then after grilling, save 4 tablespoons of the remaining juice (together with any bits of minced onion).
While you're preparing the hamburgers, sauté the minced onions, then put into a small sauce pan with the other sauce ingredients and the juice from Step 1. Simmer for about 1 minute, then it's ready.
Drizzle a generous amount on top of a fluffy, just-grilled hamburger. Sprinkle black pepper to taste to give a spicy touch.
Story Behind this Recipe
It's been my dream to make this since high school. I've tested this out over 30 times. This recipe is the result of consulting with other Hokkaido COOKPAD members, "Mazou" and "Junkmaster" (again?!).
The key is to use some of the juices from grilling the hamburgers.