Place the bacon lardon in a cool 3-quart sautee pan. Render the lardon over medium heat until the bacon is browned. Remove the lardon with a slotted spoon and set aside. Remove all but 1 tbsp of the rendered bacon fat.
Sautee the fennel and apple until they begin to soften. Add shallot and garlic and sautee for 1 minute.
Deglaze the pan with the apple cider, scraping any remaining bacon bits from the bottom of the pan. Add the IPA and bring to an aggressive simmer.
Add the mussels to the pan and place the lid on. Steam the mussels for 2 to 3 minutes, until they begin to open.
Remove the mussels from the pan and place into the serving dish. Reduce the pan sauce to the desired consistency. Remove from the sauce heat, mount with butter, and season with salt and red pepper flake.
Pour the sauce over the mussels. Sprinkle the fried bacon lardon over top. Serve with a sliced baguette and the remaining IPA.