Place a large skillet over medium heat. An oval pan can be useful for accommodating the pork loin later in the recipe.
Add the diced bacon and cook for several minutes, allowing the fat to render and the bacon to begin crisping.
Stir in the finely diced shallot and continue cooking until the bacon becomes fully crisp.
Add the spinach and toss it with the bacon and shallot mixture until the leaves wilt. Stir in the minced garlic and brandy.
Continue cooking for approximately 2 minutes, or until most of the excess liquid has evaporated.
Transfer the cooked mixture to a large bowl.
Add the diced apple, dried cranberries, sea salt, black pepper, smoked paprika, Dijon mustard, maple syrup, thyme, and rosemary.
Stir thoroughly until all of the filling ingredients are evenly incorporated.
Position the pork loin on a cutting board with the fat side facing downward.
Using a sharp chef's or carving knife, begin slicing lengthwise through the pork close to the bottom, keeping the meat approximately 1/3 to 1/4 inch thick as you cut.
When the cut reaches the opposite side, turn the loin and continue slicing back in the other direction until the pork can be opened and laid flat.
Pound the butterflied loin with a meat mallet to tenderize it and create a more even thickness.
Turn the pork so the fat side faces upward and season lightly with salt. Flip it back over before adding the filling.
Distribute the prepared filling evenly over the pork, leaving an uncovered border of approximately 1 1/2 to 2 inches along the upper edge.
Press the filling gently against the meat to help keep it in place.
Beginning at the short end, carefully roll the loin into a compact roast, finishing with the fat layer positioned on top.
Secure the rolled pork loin with kitchen twine. Begin at one end and form loops around the roast, tightening them sufficiently to hold the filling without compressing the pork excessively.
Heat a large pan over medium-high heat and add a drizzle of avocado oil.
Set the pork in the hot pan with the fat side facing downward. Sear until the exterior develops a deep golden-brown color.
Rotate the loin and continue searing until each side has been evenly browned.
Add the whole garlic cloves, fresh thyme and rosemary sprigs, and 1 cup of chicken stock.
Bring the stock to a gentle simmer, then cover the pan with a lid or tightly fitted foil.
Transfer the covered pork loin to an oven heated to 425°F (218°C).
Roast for approximately 1 hour 15 minutes, or until the center reaches an internal temperature of 160°F (71°C).
Begin checking the internal temperature after approximately 55 minutes. Remove the lid or foil halfway through roasting to encourage additional browning.
After cooking, remove the roast from the oven and spoon the hot pan broth over the pork for several minutes.
Move the loin to a carving board and allow it to rest for 15 to 30 minutes before slicing.
Pour the remaining liquid from the roasting pan through a fine-mesh strainer into a large measuring vessel. Reserve the roasted whole garlic cloves separately.
Leave the strained broth undisturbed for approximately 10 minutes so the fat can separate.
Using a baster, transfer 1 cup of the broth to a separate container.
Melt the butter in a medium saucepan over medium heat and stir in the flour. Cook the roux for 3 to 4 minutes.
Gradually whisk the measured pan broth into the roux, followed by the chicken stock, stirring until smooth.
Mash the reserved roasted garlic cloves and whisk them into the gravy.
After the pork has finished resting, carefully remove all of the kitchen twine.
Cut the stuffed pork loin into slices approximately 1/2 inch thick.
Serve the sliced roast with a generous portion of the prepared gravy.