1. Preheat oven to 350 degrees Fahrenheit. Place whole squash on a Gefen Parchment-lined cookie sheet and bake for about an hour, until soft. Cool and cut in half. Discard seeds and scoop out flesh; mash with fork.
2. In a frying pan, sauté mushrooms in oil with vinegar for about 10 minutes; add thyme at the end.
3. Gently fold mushrooms into squash (if overmixed, the squash will turn brown).
4. Place about one to two teaspoons of squash mixture on each puff pastry dough square. Fold in half to make a triangle. Seal edges with a fork.
5. Place triangles on lined cookie sheets. Brush with beaten egg and sprinkle with sesame seeds. Bake at 350 degrees Fahrenheit for 20 minutes, or until golden brown.