In a saucepan, melt the butter over a medium heat and then add the flour. Whisk vigorously. Gradually add the milk and continue whisking until the sauce coats the back of a spoon. Season and add the grated truffle. Put to one side.
In a saucepan, brown the sliced mushrooms and then the sliced garlic in the truffle oil. Add the chopped parsley, followed by the salt, pepper and paprika.
Fill each cannelloni tube with the mushroom mixture.
Pour some of the truffle béchamel in an oven dish. Arrange the cannelloni evenly. Pour the rest of the béchamel over the cannelloni and garnish with the grated Parmesan.
Bake for 30 minutes. Serve with a mixed green salad.