In a small skillet, toast the peppercorns, fennel seeds and cumin seeds. Grind them in a spice mill or with a mortar and pestle (this is my preferred method), together with the red pepper flakes. Add 2 tsp sea salt and Pimentón and stir together.
Rub the spice mixture all over the pork and refrigerate for a minimum of 6 hours, preferably overnight.
Remove the pork from the refrigerator and let sit at room temperature for 2 hours before roasting.
Chop the rosemary leaves very finely and place in a small bowl. Add 1/4 cup olive oil and let infuse while the pork is coming to room temperature.
Preheat the oven to 500ºF.
Peel and quarter the onions. Place them in a bowl large enough to hold them and toss them with the bay leaves and 2 Tbs olive oil. Season with sea salt.
Rub the pork all over with the rosemary oil.
Spread the onions and bay leaves on the bottom of a roasting pan and placce the rack of pork on top. Roast at 500ºF for 15 minutes. Reduce the oven temperature to 325ºF and continue to roast until the pork internal temperature reaches 135ºF, about 1 1/2 hours.
Transfer the meat to a cutting board and tent with foil. Let rest for 10 minutes.
Slice the pork roast between the rib bones to make 8 individual chops and serve with the roasted onions.