Vegan [Japanese-style gratin with yam and soy milk]

A very easy Japanese-style vegan gratin!
Trought
[Ingredients] 2 servings
About 300g yam (I used purple tsukune yam)
Soy milk 200g
Dashi soy sauce 3 tablespoons
1/2 tbsp vinegar
About 90 g of spinach (vegetables such as mushrooms)
Appropriate amount of vegan cheese (melting cheese for those who don't mind dairy products)
*Place in an insulated dish and bake in the oven at 170-180°C for 30-40 minutes.