Preheat the oven to 400 degrees Fahrenheit
Line the baking pan with parchment paper
In a medium saucepan, fill with water and bring the water to a boil. Add 4 eggs and boil for 7 minutes. Pour out the hot water, run cold water into the saucepan in the sink for 60 seconds to help cool the eggs. Gently peel, rinse and dry the eggs with a paper towel
Sprinkle some flour onto one of your dinner plates and roll each boiled egg into the flour and tap gently on the side of the bowl to remove excess flour. The flour helps the sausage from slipping around on the egg. Set aside.
Finely dice onion and parsley. Mix sausage, onion, sage, parsley, parmesan cheese, salt and pepper by hand in the medium bowl. Divide into 4 equal sized balls of sausage . Refrigerate for 30 minutes or more if you have time. It's easier to work with if it's cold but you can do this without the refrigeration step, just add a bit of flour to your hands.
Layout a piece of parchment paper and sprinkle some flour on it. Remove the sausage balls from the refrigerator (if you chose to refrigerate) and flatten to an even thickness with the palm or your hand to about a 5-6 inch diameter. (Using a little flour on your hands is helpful to prevent sticking.) Place the egg in the middle of each flattened ball of sausage and gently mold the sausage around each floured egg and roll it in your palms to smooth it and make sure it surrounds the egg completely without holes or breaks. It's a little hard to gauge but do your best to make it an even thickness all around. Refrigerate for 30 minutes up to overnight. This refrigeration step will help prevent splitting of the sausage. You could stop here if you are making these a day ahead.
Set up your coating station by filling your soup bowl with 1 egg whisked with 2 Tablespoons milk and 1 dinner plates with 1/2 cup bread crumbs and 1 dinner plate with 1/2 cup panko crumbs
Roll the sausage/egg combo in the bread crumbs
Roll the sausage/egg combo in the egg/milk wash
Roll the sausage/egg combo in the panko
Place onto your lined cookie sheet and bake for 45 minutes or until the sausage reads 165 and the panko is beginning to brown