Step 1: Roast the Sweet Potatoes

1. Preheat your oven to 400°F (200°C) and line a baking sheet with parchment paper.
2. Wash the sweet potatoes and pierce them several times with a fork to allow steam to escape while roasting.
3. Rub each sweet potato with olive oil and season generously with salt and pepper. Place the sweet potatoes on the prepared baking sheet.
4. Roast the sweet potatoes for 45-60 minutes, depending on their size, until they are soft and tender when pierced with a fork.

Step 2: Make the Sage Pesto

1. While the sweet potatoes are roasting, prepare the sage pesto. In a food processor, combine fresh sage leaves, basil leaves, toasted walnuts, garlic, and Parmesan cheese (if using).
2. Pulse until the ingredients are finely chopped.
3. With the food processor running, slowly drizzle in the olive oil and lemon juice. Blend until the pesto is smooth and well combined.
4. Season the pesto with salt and pepper to taste. If the pesto is too thick, you can thin it out with a little more olive oil or water. Set aside.

Step 3: Toast the Walnuts

1. Heat a dry skillet over medium heat. Add the chopped walnuts and toast them for 3-5 minutes, stirring frequently, until they are golden brown and fragrant.
2. Remove the walnuts from the skillet and set them aside to cool.

Step 4: Assemble the Stuffed Sweet Potatoes

1. Once the sweet potatoes are done roasting, remove them from the oven and let them cool slightly before handling.
2. Using a knife, carefully slice each sweet potato open lengthwise, being careful not to cut all the way through the bottom. Gently press the sides of the sweet potato to create an opening for the toppings.
3. Tear the burrata into pieces and place it inside each sweet potato, allowing the cheese to melt slightly from the warmth of the potato.
4. Drizzle each stuffed sweet potato with a generous amount of sage pesto.
5. Top with toasted walnuts for added crunch.

Step 5: Garnish and Serve

1. Garnish with a few fresh sage leaves for an added touch of herbaceous flavor, if desired.
2. Serve immediately, allowing the creamy burrata and sage pesto to blend into the sweet potatoes.