In a separate skillet, melt 3 tablespoons of butter with powdered rosemary and porcini powder. Add 2 tablespoons olive oil and the fresh mushrooms. Season to taste with salt and pepper. Cook on medium low until the mushrooms are tender.
In a large, heavy pan, melt 3 tablespoons of butter and 2 tablespoons olive oil. Add the onion and cook until translucent. Stir in the black garlic. Stir in the rice. Add the wine. Stirring constantly, reduce until all the liquid is evaporated and rice grains have a glassy translucency.
Pour a ladle-full of simmering stock into the rice. Cook and stir constantly until the stock is evaporated, then add another ladle of stock. Continue cooking and stirring and adding stock until the rice is soft but firm.
Add the mushroom base to the rice mixture. Stir in the Parmesan, remaining 2 tablespoons butter, and the mascarpone. Season to taste with salt and pepper.