You need konjac flour, milk powder (with sugar), lemon juice (pure) and soda ash (very little, the less the better).

Melt the refined konjac powder with 70℃ water (powder: water is about 1: 80, so add less water, because the refined konjac powder can only condense under alkaline conditions, so you need some soda ash), then melt the milk powder in water, add lemon juice, stir evenly and let it cool. If the milk powder is not sweet enough, you can add some sugar, which is not very high in calories.

Of course, if there is no milk powder and lemon juice, you can use yogurt instead, but you can't add yogurt.