Rehydrate the mushrooms by rinsing them, then soaking in 1-2 cups (480 ml) of hot water until softened.
In a separate saucepan, gently warm the vegetable stock over low heat; add the saffron, if using.
In a large, heavy-bottomed pot or Dutch oven, melt 2 tablespoons (30 ml / 1 fl oz) of butter or heat the oil over medium heat.
Add the minced onion and cook, stirring, until soft and translucent, about 3-5 minutes.
Add the Arborio rice to the pot.
Stir constantly for about 2 minutes until the grains are coated in fat and the edges look translucent.
Season with a pinch of salt and pepper.
Pour in the white wine and stir until it has been completely absorbed by the rice.
Drain the rehydrated porcini mushrooms (reserving the liquid!) , chop them finely, and add them to the rice.
Strain the mushroom soaking liquid through a fine-mesh sieve to remove any grit, and add about half of it to the pot.
Stir until absorbed.
Begin adding the warm stock one ladleful (about 1/2 cup / 480 ml) at a time.
Stir frequently, waiting until the liquid is almost fully absorbed before adding the next ladleful.
Continue this process, stirring often to release the rice's starches.
While the risotto cooks, heat the remaining 2-4 tablespoons (60 ml / 2 fl oz) of butter or oil in a separate skillet over medium-high heat.
Add the fresh sliced mushrooms and cook, stirring occasionally, until they are beautifully browned and slightly crisp, about 10 minutes.
After about 20-25 minutes of adding stock, start tasting the rice. It's ready when it's al dente—tender with a slight chew in the center. You may not need all of the stock.
Once the rice is cooked, remove it from the heat.
Stir in the sautéed fresh mushrooms (along with their butter/oil), and the grated Parmesan cheese.
Mix vigorously for a moment to create a creamy consistency.
Check the seasoning and add more salt and pepper if needed.
Serve immediately with extra Parmesan on the side.
Keep your stock at a gentle simmer.
Adding cold liquid will shock the rice and slow the cooking process, resulting in a less creamy texture.
Don't discard the mushroom soaking liquid!
After straining out any grit, add it to the risotto along with the stock for an extra-deep, earthy flavor boost.
