Preheat oven to 400 degrees F. Line a baking sheet with parchment paper.

Pierce potatoes with a fork; place potatoes onto prepared baking sheet. Place into oven and bake until tender, about 1 hour. Let cool completely.

Cut in half; scoop flesh into a medium bowl and mash. Transfer 1 1/2 cups to a large bowl; stir in ricotta, Parmesan, egg, 3/4 teaspoon salt and 1/4 teaspoon pepper. Add flour, 1/2 cup at a time, until a soft dough forms, being careful not to over-knead.

Working on a lightly floured surface, divide dough into 6 equal pieces. Roll each piece into a 20-inch long rope, about 1-inch in diameter, sprinkling with additional flour as needed to prevent sticking. Using a sharp knife, cut each rope into 3/4-inch bite-size pieces; transfer to baking sheet.

Bring a large pot of salted water to a boil; working in 3 batches, cook gnocchi until tender, stirring occasionally, about 4-6 minutes. Drain well and transfer to clean rimmed baking sheet.

Heat olive oil in a large skillet over medium high heat. Add gnocchi and cook until golden brown and crisp, flipping once, about 2-3 minutes per side; set aside.

Melt butter in the skillet over low heat, 1 tablespoon at a time, until butter starts to foam. Add garlic and sage, and cook, stirring frequently, until fragrant, about 1 minute. Stir in gnocchi and sprinkle with Parmesan.

Serve immediately.