Bring a large pot of water to the boil. Add the potato gnocchi and cook for 2-3 minutes. Drain the gnocchi and leave them in the colander. Return the pot to the heat.
With the pot on a medium-high heat, add the olive oil. Once hot, add the sage leaves and cook until dark and crisp (about 1 minute) then remove with metal tongs to a plate lined with paper towel.
Add the sliced mushrooms to the hot oil and cook for 3 minutes. Add the crushed garlic and continue to cook until shrunken and dark brown. Remove from the heat.
Place a frying pan over a high heat and add the cooked mushrooms to it along with the cooked gnocchi and the unsalted butter. Fry until the butter has melted and the gnocchi have warmed through.
Divide between 2 bowls and then top with the crispy sage leaves, parmesan shavings, and some salt & pepper. Serve hot.