Put rice flour in a bowl and gradually add water, mixing with chopsticks. Switch to kneading the dough by hand (but be careful - it will be hot!).
Carefully knead the dough as if making bread or mochi. If it's too watery, add a little bit more flour.
Once it's come together, remove about 1/10 of the dough and split into 3 equal portions. Add a teeny-tiny amount of food coloring to each.
Form tiny balls out of each of the 3 colored doughs (about the size of toy bullets). Cover the mold with cling wrap.
Place colored balls in the mold, then cover with white dough. Start with a small amount of dough, then add more if necessary.
Cover with the remaining cling wrap and push into the mold with your hand until the dough fully fills the mold.
Place the other half of the mold on top and press down firmly until the excess dough is squeezed out.
Prepare the steamer. Pour in enough water so that it won't evaporate during cooking. You can use a steam tray as well.
Remove the plastic wrap and the excess dough, then smooth the molded edges with a finger. Return the excess dough to the bowl.
Line the steamer with parchment paper and place the mochi molds so that they don't touch. Steam on high heat for 10~15 minutes.
Place on a cooling rack and quickly rinse with water to cool. Fan to continue cooling. If you sprinkle with water first, it will create a nice glaze.
While they're fresh out of the steamer, sprinkle soy sauce, sweetened soy sauce, or kinako powder, and enjoy. These are also good if you fry them in soy sauce like fried mochi.
Story Behind this Recipe
In Aichi, this is called "okoshimochi" and is one of the foods that is offered during the Doll's Festival. They're good freshly out of the steamer, or fried with soy sauce later. Even if you don't have a mold, you can make them as cookies.
I've made this for Doll's Festival many times. The molds are about 2,000 yen, so I borrow from a friend. Add hot water gradually until the dough is only slightly soft. I uploaded more photos of the process.