Add the water, kombu pieces, and dried bonito flakes to a medium-sized saucepan. Heat over medium until the water is just about to boil. Turn off the heat and let steep for 5 minutes. Strain out the kombu and soggy bonito flakes with a fine mesh strainer and pour the broth back into the saucepan.
Rinse the brown rice under running water and let it drain. Add the brown rice to the broth, cover, and bring to a boil over medium heat. Once it starts to boil, reduce heat to low and simmer covered for 15 minutes.
While the rice simmers, pour boiling water over the dried shiitake mushrooms and let it sit for 15 minutes. Once the mushrooms are soft, rinse them under running water and then squeeze out any excess liquid. Slice the mushrooms and set aside. Reserve the water the mushrooms soaked in for later.
After the rice has cooked 15 minutes give it a stir, making sure the rice isn’t sticking to the bottom. Cover and cook for another 15 minutes.
Add the sliced shiitake mushrooms and stir. Simmer covered for 20 minutes.
If you like your congee to be a little smoother and more broken down, keep adding a 1/2 cup to a cup of the reserved mushroom water from earlier and cook for 15 to 20 minutes more.
Once the congee is the texture you like, add the white pepper and salt. Take the sardines out of the can and tear them apart with a fork. Add to the congee and stir. Season with fish sauce to taste.
Serve with soft boiled ramen egg, a drizzle of hot chili oil or garlic chili paste, fried shallots, sliced green onions, and Stir Fried Mushrooms with Garlic and Ginger.