Cut chicken, beef, and pork into 1 inch cubes, and place in a large bowl. Stir in onions. Cover, and refrigerate overnight.Advertisement
Arrange salt pork evenly in the bottom of a 3 quart casserole dish with a cover. Layer with 1/3 of the meat mixture and 1/3 of the potatoes; season with salt and pepper. Roll out half of the pastry a little bit thicker than for a normal pie and arrange on the potato layer, cutting a small hole in the middle. Repeat with 2 more layers of meat and potatoes seasoned with salt and pepper. Cover with remaining pastry, and cut a small hole in the middle of that layer too. Slowly add enough chicken stock through the hole until liquid appears. Cover dish.
Bake at 400 degrees F (205 degrees C) for 45 minutes, or until liquid simmers. Reduce temperature to 250 degrees F (120 degrees C). Bake for 5 to 6 hours more, or until top crust is a rich golden brown.