Japanese Beef and Vegetable Hot Pot

Name: Japanese Beef and Vegetable Hot Pot
Ingredients: 1 cup dashi (see Notes) or chicken stock; ½ cup Japanese soy sauce; ½ cup mirin or sake; ¼ cup sugar; 4 ounces shirataki (see Notes) or cellophane noodles; Boiling water; 2 tablespoons vegetable oil, divided, plus more as needed; 1 pound well-marbled tender beef (sirloin tip, top sirloin, or tenderloin), sliced paper-thin across the grain, then cut into bite-sized pieces; 1 large yellow onion, halved and cut into thin crescents; 4 ounces (1 cup) fresh shiitake, enoki, or button mushrooms; 2 medium carrots, peeled and cut into ¼-inch diagonal slices (1 cup); 2 stalks celery, cut into ¼-inch diagonal slices (1 cup); 5 green onions, white and green parts, cut into 2-inch diagonal lengths; 9-ounce package broiled tofu (yakitofu), cut into 16 pieces