Place pork, fennel seeds, orange zest, salt, black pepper, Italian seasoning, red pepper flakes, and nutmeg into a bowl and stir very lightly with a fork to combine. Do not overmix. Cover and refrigerate overnight.

Check seasonings before using: Shape about 2 teaspoons sausage into a small patty and fry until brown in a skillet over medium heat. Let cool 1 to 2 minutes and taste for seasoning.

Cover a cutting board with plastic wrap. Divide sausage into 6 equal pieces, roll into a balls, and wrap each ball with plastic wrap. Press flat into patties and discard plastic.

Place a heavy skillet, such as a cast iron skillet, over medium-high heat. Cook patties in hot skillet until meat is no longer pink in the center and the sausage is browned, about 3 minutes per side. Serve immediately.