Cooking liquid: I could have used just water but it is better to use a very mild dashi broth and sake to enhance but not cover up the flavor of the matsutake. I soaked 5-7 inches of dried kelp 昆布 in about 500ml of cold water (I used filtered water) and let it stand overnight or, at least, several hours. The kelp will absorb water and assume its original state. It imparts a subtle kelp flavor to the broth. For 360 ml of rice, I used 400ml of the cooking liquid consisting of the kelp broth, 2 tbs of light colored soy sauce and 2 tbs of sake.
Rice: Many people like to add a small amount of glutenous rice (mochigome もち米) but I only used regular short grain Japanese rice from California (a brand called "Kagayaki"). I washed 2 cups (Japanese cups) or 360ml of rice. I washed the rice until the water came out clean not turbid. In the last few washes, I again used filtered water and drained the rice in a fine mesh strainer. I let it sit for 20-30 minutes. This appears to let the rice grains absorb just the right amount of water before cooking.
Cooking rice using an earthenware rice cooker: I could certainly have used my electric rice cooker but this time I used "Donabe" 土鍋 or earthenware rice cooker called "Kamado san". You can see the final product (right lower in the above image). When I removed the outer lid (see image below), I could really smell the matsutake. This type of rice cooker has an inner lid and an outer lid which make the pot act somewhat like a pressure cooker. As per the instructions that came with the cooker, I added the washed and drained rice (the original 2 Japanese cups or 360ml) and the cooking liquid (400ml). I placed the pot on a medium flame for 14 minutes and then turned off the heat and let it stand for 20 minutes.