Preheat the oven to 375°F.

Pour 1 1/2 cups hot water over mushrooms in a medium bowl and set aside to let soak until softened while you prepare the tenderloin.

Season tenderloin with dried rosemary and salt and pepper.

Lightly spray the tenderloin all over with canola oil spray.

Preheat an oven-proof skillet until you start to see wisps of smoke rising from the pan.

Add tenderloin and sear until golden brown on all sides.

Transfer the pan to the oven and roast 10 to 15 minutes to finish cooking the tenderloin.

Transfer to a plate and set aside to let rest.

Meanwhile, drain mushrooms, reserving soaking liquid, and cut into small pieces. Set aside.

Mix flour, 1 teaspoon of the truffle oil and butter in a small bowl and set aside.

Heat olive oil and 2 teaspoons of the truffle oil in a large skillet over medium heat.

Add shallots and cook for 2 to 3 minutes, until translucent.

Add mushrooms and cook for 1 minute more.

Deglaze the pan by pouring in the reserved mushroom liquid.

Bring to boil and then whisk in the butter mixture until well incorporated and the sauce begins to thicken.

Pour any juices from the resting tenderloin into the skillet along with the remaining 1 teaspoon truffle oil. Stir to combine.

Slice the tenderloin into medallions and spoon the sauce over top. Serve immediately.