Step 1

Put rice in a large saucepan and add water to cover by 1 inch. Swish with your fingers to loosen the surface starch. Pour off the water and repeat two or three times, or until the water is nearly clear. Pour the rice into a fine-mesh sieve and let drain for 5 minutes. Shake the sieve a few times, then return the rice to the pan.

Step 2

Add dashi, mirin, tamari and salt. Let stand for 30 minutes.

Step 3

Bring the mixture to a lively simmer over medium-high heat, stirring occasionally. Reduce heat to maintain a low simmer, cover and cook for 30 minutes. Place mushrooms, carrot and scallion whites on top, cover and cook until the rice and vegetables are tender, about 15 minutes more.

Step 4

Remove from heat and let stand for 10 minutes. Scatter peas over the top, then fluff the rice and combine with the peas. Cover and let stand until the peas are thawed, about 10 minutes. Stir in scallion greens before serving.