Step 1In a bowl, soak the sweet rice in water for 2 hours or overnight.
Step 2Wash the short- or medium-grain rice well in a colander or strainer. Let stand for 15 minutes to drain completely.
Step 3Drain the sweet rice and place in the donabe pot or electric rice cooker with the rinsed short- or medium-grain rice and the water to soak for 20 minutes.
Step 4Meanwhile, bring a small pot of water to a boil. Place the scallops in a strainer and slowly pour the boiling water over the pieces to blanch them slightly. Set aside.
Step 5Stir the sesame oil, soy sauce and sake into the soaked rice until combined. Top the rice with the kombu, scallops and goji berries.
Step 6When the rice has rested, remove the lid(s) and discard the kombu. Gently toss the rice, scooping the rice from the bottom up using a paddle or spatula. Season to taste with salt if desired.
Step 7Serve immediately, sprinkling the garnishes over the rice or serving them on the side.
For a single-lidded donabe: Cover with the lid and place on the stove over medium-high heat. Cook until the water comes to a slow boil, about 8 to 10 minutes. Reduce the heat to a gentle simmer over medium-low heat and cook, covered, for 10 minutes. Remove from heat and rest, covered, for 20 minutes. Try not to open the lid too often during the cooking process as this releases the steam and disrupts the cooking process.
For a double-lidded donabe: Cover with both lids (make sure the inner lid's ventilation hole is at a 90-degree angle relative to the hole on the outer lid). Place the donabe on the stove over medium-high heat. Cook until the water comes to a boil and steam comes rapidly from the outer ventilation hole. Remove from heat and rest, covered, for 20 minutes.
For an electric rice cooker: Follow the manufacturer's instructions, but make sure the rice steams at least 15 minutes with the lid closed. Rest, covered, for 20 minutes.