How to Make It
Bring a large saucepan of salted water to a boil. Add sweet potatoes and cook until tender, about 8 minutes. Drain and set aside.
Melt 1 tablespoon butter in a large skillet over medium-high. Add garlic and sage; cook until golden and fragrant, about 1 minute. Using a slotted spoon, transfer to a paper towel. Add gnocchi to skillet and cook, stirring occasionally, until golden, about 3 minutes. Add sherry and cook until reduced by half, about 2 minutes. Add stock, salt, and pepper and cook until reduced by half, about 5 minutes. Remove from heat. Add sweet potatoes and remaining 3 tablespoons butter, swirling until butter is melted.
Serve gnocchi topped with hazelnuts, garlic, and sage.