For the hot sauce: Heat the vegetable oil in a saute pan over medium heat. Add all the peppers, the garlic and shallots, and saute until softened and fragrant, 5 to 7 minutes. Then add 1/2 cup water and simmer an additional 4 to 5 minutes.
Place the cooked mixture into a blender and add the vinegars and salt. Blend until completely smooth and pureed. Adjust the seasoning.
For the compound butter: In the bowl of a food processor, with the machine running, drop in the 5 whole garlic cloves, through the feed tube, one at a time. Scrape down the garlic with a spatula and add the butter, parsley, lemon zest and juice, and 1 to 2 tablespoons of the hot sauce. Season with salt and pepper, and puree until smooth. Reserve one third of the mixture in a small bowl and set the rest aside to spread on your chicken.
For the chicken: Using your fingers, gently loosen the skin of the chicken away from the meat. Spread the compound butter under the skin as well as over the skin. Wash your hands and then sprinkle the chicken generously on both sides, using tongs to turn it over (just to prevent the mid-seasoning hand wash). Set the chicken aside for a moment.
Set a heavy-bottomed roasting pan over medium-high heat. Add the olive oil, then the chicken neck, wing tips and the sausage, and brown everything, stirring occasionally to brown all over, 8 to 10 minutes. Add the smashed garlic cloves, stir for 1 minute. Add the potatoes and toss them in the drippings. Add the pepperoncini, the pepperoncini liquid and the chicken stock. Place the spatchcocked chicken breast-side down on top of the potatoes and sausages. Roast for 30 minutes, then flip the chicken over and continue to cook until the chicken registers 160 degrees F in the thigh, about 45 more minutes. Remove the chicken from the pan, smear the remaining compound butter on top of it and leave it to rest for 15 minutes.
While the chicken rests, continue to roast the potatoes and what is left in the pan for 15 minutes more.
Once the chicken is rested, cut it into 8 to 10 pieces, however you like. I love to serve it family style and pour all the potatoes and sausage out onto a platter and place the cut up chicken on top, making sure to pour over all the juices from the cutting board where you cut your chicken. Sprinkle chopped parsley all over and dig in. Serve with more hot sauce on the side, if desired.