In a frying pan melt the butter and add the onions. Cook the onions over medium low heat. Add the salt and sugar, stirring frequently until the onions are a golden brown colour and soft. Set them aside to cool.
In a huge bowl, combine all of the ingredients, except for the buns and burger toppings. Use your hands to mix the ingredients. To make sure that everything is combining well, grab chunks with your hands and use a twisting motion. Repeat until the mixture is uniform. Chill the meat mixture for 15 to 25 minutes.
After the meat has set again, take about ¾ to 1 cup of meat mixture into your hands and form a patty that is about ½-inch thick. Lay the hamburgers out on a sheet of waxed paper for ease of use and packaging. You should get about 12 to 14 burgers. Keep in mind that they will shrink up when you cook them, so you want to make sure that they’re as big if not a little bigger than the buns you are planning to use.
Chill the burgers again for 15 to 20 minutes to set the meat.
Oil your grids and preheat your grill to medium high, about 400°F to 450°F.
Lay the burgers on your grill and cook them for about 7 minutes per side, flipping at least once, or until an instant read thermometer says 160°F. You will know they’re ready to flip when your spatula easily slides under. Remember to be gentle with these. They’re hand made and will fall apart if you didn’t oil and don’t wait until they’re ready to flip.
Serve your burgers with all the toppings you want, on fresh buns or Kaiser rolls.