For the Sliders:

• 1 1/2 pounds boneless steak (e.g., ribeye, filet, sirloin)
• Neutral oil, as needed
• Kosher salt, to taste
• Freshly cracked black pepper, to taste
• 3 sweet onions, thinly sliced
• 9 slider buns
• 3/4 pound sliced havarti cheese

For the Cowboy Butter:

• 1 stick unsalted butter, at room temperature
• 4 garlic cloves, minced
• 1/2 lemon, zested and juiced
• 1 tablespoon Dijon mustard
• 1 teaspoon paprika
• 1/2 teaspoon cayenne
• 1/2 teaspoon dried thyme
• 1 teaspoon red pepper flakes
• 1 tablespoon chives, minced
• 2 tablespoons fresh parsley, minced
• Kosher salt and pepper, to taste