On a clean surface, shape your flour into a volcano, crack the egg into the center and slowly pull the flour in with a fork.
Mix until it comes together, then knead by hand for about 10 minutes until smooth and elastic.
Shape into a ball, wrap in plastic wrap and let it rest for about 30 minutes.
Mix mashed potatoes with crispy pancetta and season with salt, pepper and a little nutmeg.
Roll the rested dough into a thin sheet (1-2mm), dusting with flour as needed.
Place small mounds of filling on one half of the sheet, fold the dough over and press gently around each to seal.
Use a pasta cutter or knife to cut into little square pillows.
Drop into salted boiling water and cook for 2-3 minutes until they float.
In a pan, melt butter with sage, garlic and basil. Toss the agnolotti gently in the sauce.
Plate and sprinkle generously with parmigiano. Serve warm and buttery.