Trim any excess fat from the steak. Rub one tablespoon of oil over one side of the steak, then repeat with the other tablespoon of oil on the other side. Sprinkle with salt and pepper, rubbing it in well. Set aside.
In a large saucepan, melt the butter over medium-low heat. Add garlic, Worcestershire sauce, Dijon, and the seasonings, stirring to combine. Add diced onions and cook for 2-3 minutes. Transfer the sauce to a bowl and set aside.
Cook the steaks to your liking in a pan or on the grill. Set aside and baste both sides with some of the sauce. Let rest for 10 minutes, then slice very thinly.
Line a baking sheet with parchment paper. Separate the slider buns and place them on the parchment. Spread a little cowboy butter sauce on the bottom buns and add a layer of cheese.
Evenly distribute the steak slices on each slider bun. Add more cheese on top of the steak. Spread some sauce on the top buns and place them on the sliders. Baste the tops with the remaining sauce.
Place the baking sheet in the oven under the broiler for 1-2 minutes, or until the cheese melts.
Serve and enjoy!
Notes
Use a tender cut like ribeye or sirloin for the best flavor and texture.
Let the steak rest for at least 10 minutes after cooking to retain its juices.
Use a meat thermometer to ensure the steak reaches your preferred doneness: 125°F for rare, 135°F for medium-rare, 145°F for medium, 150°F for medium-well, and 160°F for well-done.
Make sure to ration the cowboy butter sauce for each step: basting the cooked steak, spreading the sauce on the bottom slider buns, spreading the sauce on the top buns before assembly, and basting the top of the assembled sliders with the remaining sauce before broiling.