Cut chicken thighs into 1-inch pieces. Chop pancetta finely using a meat cleaver until paste-like in texture. Mix chicken and pancetta together. Sprinkle salt, pepper, thyme, fennel, coriander, cayenne, nutmeg, and sage. Mix until combined and place mixture on a plate; cover with plastic wrap and freeze for 15 to 20 minutes before grinding.

Peel and quarter apples. Grate apples into a bowl. Place grated apples in a paper towel and squeeze all the water out. Add apples to the partially frozen chicken sausage meat.

Place 1/2 of the chicken mixture in a food processor. Pulse on and off until mixture is slightly finer than coarse sausage. Repeat with the remaining chicken. Cover with plastic wrap and refrigerate to let the flavors develop, 4 hours to overnight.

Use a large ice cream scoop to portion out the meat. Flatten scoops with dampened hands to make patties about the same size as your biscuits.

Heat oil in a large skillet over medium-high heat. Cook patties until bottom is browned and leaves a deep brown fond in the skillet, 3 to 5 minutes. Reduce heat to medium and flip patties over. Add butter and sage leaves. Cook until patties are firm to the touch, removing leaves once they stop bubbling, about 5 minutes more. Remove patties.

Whisk flour into the pan; cook and stir until starting to thicken, about 1 minute. Pour in broth and bring to a boil, whisking the browned bits of food off the bottom of the skillet. Add maple syrup and creme fraiche; season with salt and pepper. Cook until gravy is spoonable and reaches desired thickness, 2 to 3 minutes more. Add more broth if gravy is too thick. Remove from heat.

Place biscuit halves on individual plates. Top each with a chicken sausage patty; spoon gravy on top. Garnish each with a fried sage leaf.