Cover porcini in boiling water and allow to stand 10 minutes to soften. Drain, reserving liquid. Finely chop mushrooms.
Heat oil in a large, deep frying pan over medium heat. Add leek, garlic and pancetta and sauté for 5 minutes or until pancetta starts to colour. Add mushrooms, including the porcini, and cook, stirring often, for 5 minutes or until softened. Strain the reserved porcini liquid into the pan, add the stock and simmer over medium heat for 4-5 minutes or until sauce reduces slightly.
Meanwhile, cook the pappadelle in a large saucepan of boiling salted water until al dente. Poach eggs in a separate pan of simmering water. Drain pasta and return to the hot pan. Add mushroom sauce and thyme, toss over low heat until combined.
Pile the pasta and sauce into warm bowls; top each with a poached egg. Grate over parmesan and season to taste. Serve.