Steps

1. Wash the 250g of yam with the skin on, and remove or singe off the fibrous roots.
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2. Place the prepared yam in a food-grade bag and pound it with a rolling pin until it breaks down completely.
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3. Add 1 egg, 2 tbsp of potato starch, and 1 tsp of dashi powder to the bag. Close the bag and mix well by kneading.
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4. Heat 2 tsp of vegetable oil in a frying pan over medium heat.
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5. Cut off a corner of the food-grade bag containing the yam mixture and pour it into the heated frying pan.
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6. Swirl the pan to spread the batter evenly, cover with a lid, and steam-grill over low heat for 7 minutes.
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7. After steaming for 7 minutes and the center has set, carefully transfer the mixture onto a plate.
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8. Place the frying pan upside down over the plate with the mixture, then flip them together to return the mixture to the frying pan. Reshape it into a round form.
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9. Grill over medium heat for about 1.5 to 2 minutes until the underside is browned.
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10. Once browned, carefully slide the gratin onto a serving plate as it is quite soft and prone to breaking. KEY TIP: After steam-grilling, transfer the mixture to a plate and then use the frying pan to flip it back into the pan. This helps to flip it cleanly without breaking the shape.
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11. Drizzle with your preferred amount of mentsuyu or dashi soy sauce, and sprinkle bonito flakes all over.
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12. Garnish the center with chopped scallions to complete. KEY TIP: Serving with mayonnaise on the side adds richness and enhances the flavor.
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