In a small saucepan, combine the dried porcini mushrooms with the stock and warm over low heat while you begin the rice.
Heat 3 tablespoons (45 ml / 1.5 fl oz) of the olive oil in a deep skillet or pot with a lid over medium-high heat.
Add the brown basmati rice and cook, stirring occasionally, until it smells nutty and begins to brown, about 10 minutes.
Stir in the sliced onion and the softened porcini mushrooms (reserving their soaking liquid).
Season with salt and pepper and continue to cook, stirring, until the onion softens, about 5 minutes.
Pour the porcini-infused stock into the skillet all at once.
Bring the mixture to a gentle simmer, then reduce the heat to low, cover, and cook for about 40 minutes.
Check after 20 and 30 minutes to ensure there is enough liquid, adding about 1/2 cup (480 ml) of water if it looks dry.
About 15 minutes before the rice is done, heat the remaining 3 tablespoons (45 ml / 1.5 fl oz) of oil in a separate skillet over medium-high heat.
Add the sliced shiitakes, a generous pinch of salt, and a few grinds of pepper.
Cook, stirring occasionally, until the mushrooms are browned and slightly crisp, about 10 minutes.
Once the rice is tender, uncover the pot and cook for a minute or two to evaporate any remaining liquid. Gently stir in the crispy shiitake mushrooms, taste for seasoning, and adjust if necessary.
Serve immediately.
Don't skip toasting the dry rice in oil before adding any liquid. This step is crucial for developing a deep, nutty flavor and improving the final texture.
