Mix together the softened butter, minced garlic, and chopped dill until well combined. Set aside.

Thinly slice the steak. Pro tip: slightly freeze the steak before slicing to make it easier.

Heat a skillet with oil over high heat. Add the steak strips and season with salt. Cook until just browned, then remove from the skillet and set aside.

Slice the onion into half rings. Using the same skillet, sauté the onions until golden brown. Remove from heat and set aside.

Cut the baguette lengthwise and spread the herb butter on both sides. Layer the steak slices, sautéed onions, and Havarti cheese slices on the bread.

Keep the sandwich open-faced and broil for about 2 minutes, or until the cheese is melted and bubbly.

Serve immediately while still warm.