Prepare Steaks: Trim any excess fat or silver skin from the steaks. Rub the steaks lightly with neutral oil. Season generously on all sides with kosher salt and freshly cracked black pepper. If the steaks are thick, season more heavily. (Optional: For deeper seasoning, wrap the seasoned steaks in plastic wrap and refrigerate for a few hours before cooking).

Make Cowboy Butter:

• In a small saucepan over low heat, melt the 1 stick of room temperature butter. Whisk continually.
• Add the lemon juice, lemon zest, minced garlic, Dijon mustard, paprika, cayenne pepper, dried thyme, and red pepper flakes. Whisk to combine.
• Remove the saucepan from the heat. Stir in the minced chives and minced parsley. Season with salt and pepper to taste.
• Spoon out a few tablespoons of the Cowboy Butter into a small bowl for brushing the steaks while grilling. Set aside the remaining butter for the slider buns.

Cook Steak:

• Preheat your grill to medium-high heat, setting up both direct and indirect heat zones.
• Remove steaks from the refrigerator (if chilled) and let them rest at room temperature for 30 minutes before grilling.
• Place the steaks over direct heat. Grill for about 2-3 minutes per side, developing a good sear. If flare-ups occur, move the steaks to the indirect heat zone until the flames subside.
• Brush both sides of the steaks with the reserved Cowboy Butter as they cook.
• After 5-6 minutes of total direct heat cooking, move the steaks to the indirect heat zone. Continue cooking until the steaks reach your desired internal temperature (use a meat thermometer).
• Remove the steaks from the grill and transfer them to a cutting board. Tent loosely with foil and let them rest for 10 minutes before slicing.

Caramelize Onions:

• While the steaks are resting, place a cast-iron skillet on the grill grates over direct heat (or use a skillet on the stovetop).
• Add 2-3 tablespoons of butter to the skillet. Once melted, add the thinly sliced sweet onions.
• Cook the onions, stirring occasionally, until they are deeply caramelized and sweet, about 15-20 minutes. Adjust heat as needed to prevent burning.

Prepare & Assemble Sliders:

• Preheat your oven’s broiler. Line a baking sheet with parchment paper.
• Separate the tops and bottoms of the slider buns.
• Brush the inside of both the top and bottom slider buns with the remaining Cowboy Butter.
• Place the bottom buns on the prepared baking sheet. Layer the grilled caramelized onions evenly over the bottom buns. Top the onions with half of the Havarti cheese slices.
• Place the top buns (butter-side up) on the baking sheet alongside the bottom buns. Top them with the remaining Havarti cheese slices.
• Thinly slice the rested steak against the grain. Place a few strips of sliced steak on top of the onions and cheese on the bottom slider buns.
• Place the baking sheet under the broiler for 1-2 minutes, or just until the cheese begins to melt and bubble. Watch carefully to prevent burning.
• Remove the baking sheet from the oven. Carefully place the top slider buns (with melted cheese) over the steak on the bottom buns.
• Slice between the buns to separate the sliders. Serve immediately.