Preheat oven to 400 degrees.
Roast sweet potato for 40-45 minutes or until fork-tender. Alternatively, place sweet potato in a bowl and cover with plastic wrap. Microwave for 8-10 minutes or until fork-tender. Remove peel and mash until smooth. Let cool completely.
Add ricotta to mashed sweet potato and mix until combined. Add egg and salt, mixing until combined. Gradually add 1 ½ cups flour, mixing until combined. The dough will be sticky but not loose. Add flour 1 tablespoon at a time if still very moist, mixing until well combined.
Generously dust counters with flour and scrape dough onto counter. Cut dough into 4 sections. Start with the first piece and roll into a ¾ inch thick rope. Use a knife and cut log into ¾ inch wide bite-size pieces. Transfer cut gnocchi onto a baking sheet dusted with flour. Repeat with remaining dough.
Prepare sauce. Melt butter in a saucepan over medium heat. Heat until butter turns into a golden brown color and smells nutty, about 3 minutes. Reduce heat to low, add sage and simmer for 1 minute. Keep warm.
Bring a medium pot of salted water to a boil over high heat. Add gnocchi and cook until they float to the top, about 3-4 minutes. Use slotted spoon to remove gnocchi from water and immediately place them in browned butter sauce. Season pasta with salt and pepper. Transfer to serving bowls and top with fresh arugula, toasted pinenuts, and grated parmesan. Serve immediately.