To make the pastry, place the flour and salt in a food processor. Add in the cold butter and pulse, until it resembles coarse crumbs. Slowly add in the water and pulse, until a dough forms. Wrap in plastic and refrigerate 1 hour.
Heat the butter in a skillet over medium low heat. Add in the onions and sprinkle with salt. Cook, stirring occasionally, about 10 minutes, or until onions are golden and caramelized.
In a large bowl, combine the pumpkin, onions, garlic powder, thyme, salt, pepper, and cheddar cheese.
Cut the pastry dough into 4 equal pieces. Roll each into a 6 inch circle.
Place 1/4 cup of the pumpkin mixture on one side of each circle of dough. Brush the edges with water, and fold over to create a half moon shape. Crimp the edges together to seal.
Brush the tops with egg wash, and cut 3 small slits in the top of each.
Bake at 400 degrees for 25-35 minutes.
