1. In a large pan, heat the olive oil over medium heat for one minute. Add the onions and reduce the heat to medium low. Cook gently, stirring often, until the onions become translucent. (Caramelizing onions can take a couple of hours, so be patient.)
2. Once the onions have begun to cook down and are translucent, add the salt and white sugar. Continue to cook the onions over medium-low to medium heat, stirring often, until they’re caramel brown. Remove from the heat and set aside.
3. Slice the Hawaiian rolls to make sandwich buns. Place the bottom halves in two 9×12 baking dishes (you may want to line the dishes with foil for easier cleanup). Top the bottom halves of the rolls with the deli meat and then a slice of cheese. Spoon the caramelized onions onto each sandwich. Top each sandwich with the top half of the roll.
4. In a small pot, combine the butter, brown sugar, onion powder, mustard, and Worcestershire sauce. Heat over medium-high heat and whisk until combined. Allow the mixture to simmer for one minute, stirring occasionally, then remove from heat. Pour the sauce evenly over the sandwiches.
5. Allow the sandwiches to sit for at least 15 minutes before baking to absorb the sauce. You could also cover the pans with plastic wrap and refrigerate the sandwiches for up to 24 hours before baking.
6. Bake the sandwiches at 350 for about 20 minutes.
Makes 24 slider sandwiches (8-12 servings)