Prepare the Herb Butter: In a medium bowl, combine ½ cup softened unsalted butter with 2 cloves of minced garlic and 2 tablespoons of chopped fresh dill. Mix until smooth and well-blended, then set aside to meld for about 10 minutes.

Slice the Steak: Take 1 pound of well-marbled steak, slice it into thin strips against the grain. Chill the steak in the freezer for 15–20 minutes for easier slicing.

Cook the Steak: Heat 2 tablespoons of oil in a large skillet over high heat. Season steak with salt and pepper, add to the skillet, and sear for 2–3 minutes on each side, then set aside.

Caramelize the Onions: In the same skillet, lower heat to medium, add 2 sliced onions, and cook for about 10 minutes until caramelized, adding water if needed to prevent sticking.

Assemble the Sandwich: Slice the baguette and spread herb butter on each half, then layer with steak strips, caramelized onions, and Havarti cheese.

Broil the Sandwich: Preheat broiler and broil assembled sandwich for 2–3 minutes until cheese is melted and bubbly, keeping an eye on it to prevent burning.

Serve the Sandwich: Remove from oven, cool slightly, slice into portions, and serve hot.