In the bowl of a stand mixer fitted with the beater attachment, combine the ground pork, onion, crushed fennel seeds, salt, pressed garlic, and black pepper. Mix on low speed for 4 minutes.
Peel, core, and shred the apples. Place the shredded apples in a flour sack towel and squeeze out as much juice as possible.
Measure 2 cups of the squeezed shredded apples and add them to the pork mixture. Mix on low speed for 2 minutes, or until the apples are evenly incorporated.
Transfer the sausage mixture to an airtight container and refrigerate for at least 8 hours or overnight.
Divide the mixture into 10 equal portions and shape each into a patty.
Heat a skillet over low heat. Cook the patties until nearly cooked through, then increase the heat to medium and brown both sides until cooked through.
Serve immediately, or cool and refrigerate or freeze for later use.
Notes
Crush the fennel seeds just before mixing for the freshest flavor.
Shred and squeeze the apples immediately before adding them to the sausage mixture to prevent browning and remove excess moisture.
Refrigerating the sausage mixture overnight improves both the flavor and texture, but an 8-hour chill is sufficient.
Freeze the sausage mixture in bulk, or shape it into patties before freezing. If freezing patties, freeze them in a single layer until firm before transferring them to a freezer-safe container or freezer bag to prevent sticking.
Store cooked sausage in an airtight container in the refrigerator for up to 4 days. Reheat gently in a skillet over low heat until warmed through.