Aside from iyokan, oranges or dekopon also work well for this recipe. Kawachibankan (Japanese pomelo) works too Adjust the quantity of sugar you use in accordance with the sweetness of the fruit.
Dissolve the powdered gelatin in two tablespoons of water.
Carefully remove the thin skin around the pulp. Mash half the pulp finely and the rest roughly.
Put the iyokan in a measuring cup. There should be about 300 ml when lightly compacted into the cup.
Sprinkle on sugar evenly and mix until it dissolves, then add the water up to the 400 ml mark.
Heat the expanded gelatin in a microwave until it feels warm to the touch, then add Step 5 bit by bit while mixing quickly.
If you want, add a teaspoon of Cointreau. Fill the cups and refrigerate. It's done when they're nice and firm.
It'll set firmly, you could use it as a layer on a cake.
Story Behind this Recipe
I made this classic jello for my family, who prefers their jello on the firm side. I've been making this with Kawachibankan (Japanese pomelo).
If you don't use a lot of iyokan, it doesn't look grea, so when you add water make sure it's enough to cover the fruit. In Step 6, if the iyokan is too cold, the gelatin will probably set with lumps, so warm slightly in the microwave just to be safe.