To bake the sweet potato: Preheat the oven to 400. Wash and dry the sweet potato. Wrap the sweet potato with aluminium foil and pierce with a fork. Place the potato on a baking sheet and bake for 35- 40 minutes. Remove potato from oven and check to be sure it's fork tender. Allow it to cool a bit and then remove the skin. Mash until smooth with a potato masher.To Microwave the sweet potato: Wash and dry the sweet potato. PIerce it in a few spots with a fork. Place the sweet potato on a paper towel-lined plate. Microwave on high for 3 minutes. Turn the plate and repeat. Check to make sure it's fork tender. Allow it to cool a bit and then remove the skin. Mash until smooth with a potato masher. Cook the pasta according to package directions. If you want to add the peas, in the last 2 minutes of the pasta's cooking time, add the frozen peas. Drain the pasta (and peas). Stir in 1 tbsp of olive oil and set aside.
In a large sauce pan over medium heat, add the butter. When it foams, add the flour and whisk until combined. Allow it to cook for a minute.
Add the milk slowly, stirring continually to eliminate lumps. Stir until it thickens, when it clings to the back of the spoon.
Turn off the heat and add the cheese. Stir until they melt.
Add the sweet potato puree and stir until combined.
Taste and season with salt and pepper
Serve with an extra sprinkle of parmesan cheese.