For White BBQ Sauce, whisk together Duke’s Mayo, Apple Cider Vinegar, Mustard, Prepared Horseradish, Garlic Cloves Minced Fine, Worcestershire Sauce, Celery Seeds, Smoked Paprika, and salt and pepper.
Chill for at least 30 minutes. Best if made a day ahead.
For Pork Belly, Rinse the pork belly whole, then place into a pot, covering it completely in cold water. Bring the water to a moderate boil, and cook pork for 10 minutes to remove scum. Discard cooking water.
Place the pork into a hotel pan add enough water to cover half the meat. Add rice wine, soy sauce, gochujang, ginger, garlic, sugar and sesame oil. Cook in a 325 F oven for 1 ½ to 2 hours, flipping the meat a few times. Check to see if the meat is tender but not falling apart. Take out pork belly and let cool.
Meanwhile, take the skin off the eel. Mix the gochujang, mirin and honey together to make a glaze. Brush the top of the eel with the gochujang and bake in a 325 F oven for 15 minutes.
Cut pork belly into pieces about 1 inch by ½ inch. Cut the ell the exact same size and stack the eel on top of the pork belly. Top with the white BBQ sauce and garnish with the raw button mushrooms.