Hi Jeffrey - here is a recipe from Bon Appetit on the Epicurious site. There were lots of "reviews," most of which said they doubled the wasabi and liked it better that way. Here is the recipe as printed:

WASABI MASHED POTATOES

3 pounds russet potatoes, peeled, cut into 2-inch pieces

3/4 cup whole milk
1 tablespoon wasabi powder
1/4 cup (1/2 stick) butter

Place potatoes in large pot of cold salted water. Boil until tender, about 20 minutes. Drain. Return to pot; mash.

Combine 3/4 cup milk and 1 tablespoon wasabi powder in small bowl. Stir to dissolve powder. Add milk mixture and butter to potatoes. Using electric mixer, beat potatoes until fluffy and smooth. Season potatoes to taste with salt and pepper. (Can be prepared 2 hours ahead. Cover and keep at room temperature. Rewarm mashed potatoes over low heat, stirring frequently.)

Serves 6 as a side-dish.