Prepare Caramelized Onions: Heat the olive oil in a large skillet over medium heat. Add sliced onions and sprinkle with salt. Reduce the heat to medium-low and cook, stirring occasionally, for about 25 minutes until the onions are deeply golden and jammy. Remove from heat and allow to cool slightly.
Preheat the Oven: Preheat your oven to 350°F.
Make the Poppy Butter Topping: In a medium bowl, combine the melted butter, poppy seeds, minced garlic, and Worcestershire sauce. Stir until well mixed.
Assemble the Sliders: Split the slider buns in half horizontally and place the bottom halves on a baking sheet. Spread a thin, even layer of mayonnaise over the bottom buns. Layer half of the turkey slices on the buns, followed by the Swiss cheese, and then the remaining turkey slices. Spread honey mustard over the turkey slices and top with the caramelized onions. Place the top halves of the buns on the sliders.
Apply Poppy Butter: Liberally brush the tops of the buns with the poppy butter mixture, making sure they are fully coated.
Bake: Place the sliders in the oven and bake for 10 to 12 minutes, or until the cheese has melted and the buns are golden brown.
Serve Hot: Take them out of the oven and serve right away. These sliders are ideal for parties or a quick dinner!
Enjoy the irresistible combination of sweet caramelized onions, and savory gooey Swiss cheese!