Toast the hazelnuts in a non-sticking pan for a couple of minutes until lightly golden and set aside. Clean the mushrooms cutting the fibrous part at the base of the stem off and using a small knife, remove any leftover soil residue. Wash the mushrooms thoroughly under running water and drain.
Heat 4 tblsp of oil in a pan, add the garlic clove ant cook until fragrant about one minute. Add 1 sprig of rosemary and the mushrooms and sauté on medium high flame for about 5 minutes. Season with salt and pepper, discard the rosemary, add the hot broth and cook for 2 more minutes.
Drain a handful of mushrooms with a slotted spoon and set aside. Blend remaining mushrooms and broth with an immersion blender to obtain a fluid smooth cream. If necessariy add a little more broth according to your taste.
In the meantime cook the Tortelloni according to package instructions and heat 4 tablespoons of oil with the mushrooms and remaining rosemary cut in small sprigs. Divide the cream in the plates. Drain the tortelloni and add to the plates. Garnish with mushrooms, tosted hazelnuts and rosemary sprigs. Season with hot oli and serve.