Optional: Add fennel, sage, and marjoram to a clean pan over medium heat. Cook for 1-2 minutes until toasted and fragrant. Remove from the pan and let cool. Add red pepper flakes (if using) along with the other toasted spices to a spice grinder (or mortar and pestle) and crush or grind into a powder to be used in the next step.
Thoroughly combine all ingredients in a mixing bowl. Cover and refrigerate for at least an hour (preferably overnight) to allow the flavors to come together.
When ready to cook: form patties that are 2-3" wide and no more than ½" thick.
Heat pan over medium heat and add patties. Cook for 3-4 minutes on one side, flip, then cook for another 3 minutes. Cook in batches, if necessary.
Line a plate with paper towel to help drain excess oil from the cooked sausage.
Notes
This recipe can also be used for sausage pieces to be used in quiche or a breakfast scramble. Just skip the step where you form the ground meat into patties.