Simmer the sauce. In a medium pot over medium heat, stir together the ketchup, maple syrup and molasses. Simmer for 2 to 3 minutes.
Blend and add to sauce. Meanwhile, add the pineapple, garlic, spiced rum, mustard, Worcestershire sauce, salt, pepper, ginger, and cayenne pepper to a high-powered blender and blend until smooth. Transfer the blended ingredients to the simmering sauce and stir for 3 to 4 minutes more. Then turn off the heat.
Prep the sheet pan. Line a large baking sheet with aluminum foil with enough overhang to wrap the ribs. Pro tip: I like to double layer the aluminum foil, to prevent any leaks.
Prep the ribs. Preheat the oven to 275°F (135°C). Remove the thin membrane on the underside of the ribs. Pro tip: You can also ask the butcher to do this when you buy your ribs. Then place the ribs on the foil-lined baking sheet.
Bake the ribs in the oven. Take 1 cup of the sauce and mix it with an equal amount of water. Pour this on top of and around the ribs, then lightly wrap the foil around them. Bake the ribs for 3 hours. This process steams the meat, making it incredibly tender while infusing it with flavor.
Option 1: Finish the ribs on the grill (my preferred method). Preheat an outdoor grill to medium-high heat. After the ribs have finished cooking, use tongs to transfer them to a large platter to carry them to your grill. Note that the ribs will be VERY tender (i.e. fall apart tender) so I recommend using two tongs for stability. Use the remaining sauce to generously brush both sides of the ribs. Place the ribs on the grill and cook for 3 to 4 minutes on each side. Brush additional sauce as desired while grilling, then slice and serve immediately.
Option 2: Finish the ribs in the oven. After the ribs have finished cooking, remove them from the oven and carefully discard the aluminum foil with watered-down sauce. Place the ribs back on the baking sheet and use the remaining sauce to generously brush both sides of the ribs. Broil the ribs (meat side up) for 3 to 4 minutes, until the sauce begins to caramelize. Brush additional sauce as desired while broiling, then slice and serve immediately.