Preheat the oven to 350 degrees. Combine the olive oil and butter in a skillet and heat over medium heat. Add the onions and cook, stirring, until soft. Remove from the heat. Arrange two layers of the potatoes around a 9-inch pie or quiche pan that has been sprayed with a non-stick coating. Spread the onions evenly over the potatoes. Layer the remaining potatoes on top. Pour the broth over the top. Cover and bake 1 hour. Uncover and sprinkle parsley. Bake uncovered for 10 to 15 minutes. Let stand 10 minutes, then cut into pie-shaped wedges.