Soften unsalted butter in a mixing bowl, then mix in crushed garlic and chopped dill. Set aside to meld flavors.

Chill ribeye steak for 15 minutes, slice against the grain into thin strips.

Preheat a skillet over high heat, add sliced ribeye, season with salt, and cook for 2-3 minutes on each side until golden brown. Remove to rest.

In the same skillet, add sliced onion and sauté over medium heat for 8-10 minutes until caramelized. Remove from heat.

Cut baguette lengthwise, spread herb garlic butter on both halves, layer with ribeye, sautéed onions, and havarti cheese.

Preheat broiler, place sandwich open-faced on a baking sheet and broil for about 2 minutes until cheese is bubbling.

Remove, close the sandwich, slice in half, and serve immediately.