1. Preheat the oven to 375˚F (190˚C).
2. Heat the oil in a frying pan on high heat. Sauté the onions and mushrooms for 5 minutes, stirring often. Stir in the chicken stock and cream, and bring to a boil.
3. Lower the heat to medium-high. Reduce, uncovered, for 8 minutes, stirring often. Add the chopped bacon, and season with salt and pepper, to taste. Stir and set aside.
4. Sprinkle flour on a work surface and roll out the puff pastry dough to a thickness of 5 mm (1/4 in.). Cut into 4 rectangles and spread the mushroom mixture on half of each rectangle.
5. Brush beaten egg on the edges and fold over the puff pastry, pressing the edges together securely with your fingers or a fork.
6. Brush beaten egg on top of the puff pastries. Place them on a cookie sheet and bake for 40 minutes or until crisp and golden brown.
7. Serve as an appetizer on a bed of greens.

Variation: For delicious bite-sized hors d'oeuvres, cut the puff pastry dough into 12 rectangles and bake for about 25 minutes.