In a small mixing bowl, combine 4 tablespoons of softened unsalted butter with 2 crushed garlic cloves and 2 tablespoons of finely chopped fresh dill. Mix until fully blended and smooth. Set aside.

Place your 1-pound ribeye steak in the freezer for about 30 minutes; this makes it easier to slice thinly. After chilling, slice the steak into thin strips and season generously with salt. In a preheated skillet over high heat, sear the steak for about 3-4 minutes until golden brown and just cooked through, then remove from the skillet and set aside.

Using the same skillet, add your sliced large yellow onion. Cook over medium heat, stirring occasionally, for about 8-10 minutes until the onions have caramelized to a deep golden brown. Remove from heat.

Take a crusty baguette and slice it lengthwise, creating a pocket. Spread the prepared herb butter on both inner sides of the baguette. Layer the thinly sliced steak on the bottom half, followed by the sautéed onions, and finish with 4 slices of Havarti cheese.

Preheat your broiler. Place the assembled steak sandwich on a baking sheet and broil for about 2-3 minutes, keeping a close eye on it until the cheese is bubbly and melted.

Remove the sandwich from the oven and let it cool for just a minute before slicing it into manageable portions. Serve while warm.