Ham Goo Sandwiches

0 Preheat the oven to 350°F. Line a baking sheet with parchment paper, and set aside.
1 Measure the olive oil and butter into a saucepan. Warm over medium heat. Once the butter has melted, add the chopped onion. Cook until softened, about 2-3 minutes. Then stir in the poppyseeds, Worcestershire and mustard and remove from the heat to let cool while you assemble the slideres.
2 Cut the rolls in half. Place the bottom half of the rolls on the prepared baking sheet.
3 Layer the ham slices on top of the rolls, then top with the Swiss cheese.
4 Pour half of the onion sauce directly on top of the cheese, then place the roll tops on top. Pour the rest of the sauce on top of the rolls. 
7 Cover with foil, and bake for 20 minutes in the preheated oven.
5 Remove the foil, and bake for about 10-15 minutes more minutes, or until the tops are slightly brown and the cheese is melted.
6 Enjoy warm!