Pour ½ cup of boiling water over the porcini mushrooms and let soak for 20-30 minutes. Remove the mushrooms and mince them. Strain the liquid through a fine mesh strainer and add to a medium saucepan.
Add the chicken stock and 2 ½ cups water to the mushroom liquid and heat to a simmer over medium-high heat. Turn heat to low and let barely simmer.
Heat oven to 200. Melt 2 tablespoons of the butter in a medium skillet and and add the cremini mushrooms and ½ teaspoon of salt. Cook, stirring occasionally until the mushrooms are golden, about 5-6 minutes. Add the garlic and thyme and cook for 1 more minute. Scoop out the mushrooms and place in an oven safe bowl in the oven to keep warm.
Turn off the heat on the skillet and add ½ cup of the warm broth mixture to the skillet. Scrape up any browned bits and add them back into the broth.
Melt 4 tablespoons of butter in a 4 quart saucepan. Add onion and ½ teaspoon of salt and cook until softened, about 9 minutes. Add the rice and stir to coat. Cook until translucent on the edges, about 4 minutes. Add the wine and stir frequently until it is absorbed, about 2 minutes. Add the porcini mushrooms and 3 cups of the stock and cook stirring occasionally until it is absorbed, about 10-12 minutes.
Keep adding the stock, ½ cup at a time as needed after the liquid is absorbed. Cooking until the rice is cooked through, about 10-12 minutes, stirring frequently.
Add the cremini mushrooms and the Parmesan cheese. Stir and adjust seasonings.