Peel potatoes, rinse, and cut into 2-inch chunks. In a 3- to 4-quart pan, combine potatoes and broth. Cover and bring to a boil over high heat. Simmer until potatoes mash easily, 20 to 25 minutes. Drain, reserving broth. Put 3/4 cup broth and parsley in a blender. Whirl until smooth. Add parsley mixture and 1 tablespoon wasabi paste to potatoes. Beat with a mixer or mash with a potato masher until smooth, adding more broth to make potatoes as creamy as you like. Season to taste with salt and more wasabi. And for a smoother texture, mix in whipping cream.