Preheat your oven to 400°F (200°C). Scrub the sweet potatoes, pat them dry, and prick them several times with a fork. Rub them with 1 tablespoon of olive oil, salt, and pepper. Place on a baking sheet and bake for 45-60 minutes, until they are very tender when pierced with a fork. Let them cool for about 10 minutes.

While the potatoes bake, heat 2 tablespoons of olive oil in a skillet over medium heat. Add the minced garlic and cook for 30 seconds until fragrant. Add the spinach (in batches if needed) and cook until wilted, about 3-5 minutes. Remove from heat, let it cool slightly, then squeeze out all excess liquid. Chop the spinach finely.

Slice the cooled sweet potatoes in half lengthwise. Carefully scoop out most of the flesh, leaving about a 1/4-inch border inside the skin. Place the scooped-out flesh in a large mixing bowl.

To the bowl with the sweet potato flesh, add the ricotta cheese, chopped spinach, Parmesan cheese, lemon zest, nutmeg, 1/2 tsp salt, and 1/4 tsp pepper. Mash and mix everything together until well combined.

Spoon the filling mixture evenly back into the sweet potato skins, mounding it on top. Sprinkle with extra Parmesan cheese if desired.

Return the stuffed potatoes to the oven and bake for another 10-15 minutes, or until the filling is heated through and the tops are slightly golden.

Remove from the oven and let cool for a minute. Garnish with toasted pine nuts and fresh chives before serving.