Start by making the herb butter. In a bowl, mix the softened butter with the minced garlic and chopped dill until it's well blended. Set this delightful mixture aside.

Slice the steak into thin strips. A little tip: pop the steak in the freezer for about 15 minutes to make slicing easier.

Heat a skillet over high heat and add the oil. Once hot, toss in the steak and season it generously with salt. Cook until the steak is golden, then remove it from the skillet and set aside.

In the same skillet, add the sliced onion. Sauté them until they turn a lovely golden brown, then take them off the heat and set aside.

Slice the baguette lengthwise and spread the herb butter on both sides. Layer on the steak strips, followed by the sautéed onions, and top it all with the Havarti cheese slices.

Keep the sandwich open and place it under the broiler for about 2 minutes, or until the cheese is bubbly and melted.

Serve immediately while it's warm and oh-so-delicious! Enjoy every bite!