Preheat griddle to about 350-375℉. Or if cooking on a stovetop, heat a large skillet over medium heat.
*Optional - If making caramelized onions instead of the bacon jam, cook the onions on the griddle first. Cook until onions are tender and golden brown in color. Then remove from the griddle and set aside.
Portion the sausage into two equally sized balls, about 3-3.5 ounces each. When griddle or skillet is hot, place the sausage balls down on the hot surface, and use a burger press or a stiff spatula to press down until the sausage patty is evenly thin and flat (similar to cooking a smash burger).
Cook the sausage patties until about halfway cooked through (about 3-4 minutes depending on the griddle temp). Then, flip to the second side. Immediately after flipping the patties, top each with one slice of Swiss cheese and one slice of cheddar cheese.
When the sausage is cooked through and the cheese is melted, remove the sausage patties from the griddle or skillet and set aside. Or move to a cooler zone on the griddle while the eggs and toast finish cooking. *If needed, you can use a melting dome to help the cheese melt faster.
While the sausage is cooking, butter the bread and toast on the griddle until golden brown. Then, remove from the griddle.
Adjust the griddle or skillet temperature to medium-low, about 300-325℉. Cook the eggs until over-easy or over-medium, based on preference.
Assemble the patty melt. Add the smashed sausage patty and melted cheese to the bottom bread, top with the egg, and add some bacon onion jam or caramelized onions on top. Add the top slice of toasted bread. Serve warm.