Step 1Heat the oven to 350 degrees. Cut the squashes in half and remove the seeds. Set them cut side down on a baking dish covered with aluminum foil, add water to half fill and bake until the squashes are soft, about 1 hour.
Step 2While the squashes are baking, heat the oil in a small skillet and saute the onion over medium heat until translucent, about 8 to 10 minutes. Add the parsley, stir and remove from the heat.
Step 3Process the bread to fine crumbs in a blender (you should have about 1/2 cup), add the 2 tablespoons melted butter, process together and set aside.
Step 4Process the onion and parsley until well chopped. Scrape out the squash flesh, leaving about three-fourths inch next to the shell. Add the squash flesh to the onion and parsley along with the 1/4 cup butter, the sour cream and the egg and process until smooth. Season to taste with salt and pepper.
Step 5Fill the acorn squash shells with this puree and top with the buttered bread crumbs. Set cut side up on a buttered baking dish and bake until the filling is somewhat set and the crumbs are brown, 25 to 30 minutes.