Mix agar-agar powder with 1/2 cup water in a saucepan over low heat. Simmer until agar is fully dissolved, about 7 minutes.
Drain and rinse cashews. Place cashews, remaining 1/2 cup water, nutritional yeast, lemon juice, arrowroot powder, garlic, salt, and turmeric in a blender; blend until smooth and creamy, about 10 minutes.
Pour cashew cream into agar-agar mixture; bring to a boil until a thicker batter forms, about 5 minutes. Spread into 2 ramekins and chill in the refrigerator for 1 hour.