Beef Donburi with Shiso Garlic Soy Sauce

Bahan-bahan (3 porsi)

• ½ onion ((thinly sliced))
• 1 potato ((cut into thin strips))
• neutral oil ((for sautéing) )
• ¾ lb thinly sliced beef (such as ribeye)
• 1 Tbsp sake
• 1 tsp garlic powder
• ¼ tsp sea salt
• freshly ground black pepper
• 1 Tbsp potato starch or cornstarch
• 2 Tbsp sugar
• 3 Tbsp Homemade Shiso Garlic Soy Sauce
• 3 servings cooked Japanese short-grain rice ((typically 1⅔ cups (250 g) per donburi serving))