Bring mirin, sake, dashi and sugar to a simmer and stir until sugar is dissolved. Remove from heat and reserve.

Arrange beef and tofu on separate platters (or dinner plates) cover with plastic wrap and refrigerate. Arrange mushrooms, onion, scallions, and bok choy on a serving platter and set aside.

Rinse rice in a fine mesh strainer until water runs clear. Place in a small pot and cover with 2 cups water, bring to a simmer then turn heat to low and cover with tight fitting lid. Steam until all the water is absorbed, about 30 minutes.

Set up butane burner or electric hot plate, and carefully ignite. Place a thick bottomed, low sided pan over burner and pour in sauce mixture. Bring to a simmer

Divide rice between 4 small bowls. Place platters of ingredients around burner and cook as you eat by transferring to simmering broth and cooking to desired doneness. If desired, break egg into separate bowl, beat and use to dip steaming hot ingredients into.