Sauté the finely chopped onion in olive oil until soft.
Add ¾ of the mushrooms and cook until their moisture evaporates and they lightly brown.
Add crushed garlic and thyme; sauté briefly.
Stir in soy sauce, let it evaporate, then transfer the mushrooms to a separate bowl.
Dissolve the bouillon cubes in water, bring to a boil, and keep the broth hot over low heat.
In the same pan, sauté the remaining mushrooms with the onion.
Add the rice and cook for about 1 minute, stirring constantly.
Pour in the wine and let it fully absorb.
Add hot broth one ladle at a time, stirring continuously, until the rice is al dente.
Remove from heat and stir in the reserved mushrooms, Parmesan, butter, and parsley. Season with black pepper and serve immediately.