Begin by heating olive oil and butter in a skillet over medium heat. Watch for the butter to melt and sizzle, creating a flavorful base for your mushrooms.

Add sliced mushrooms to the skillet, stirring occasionally. Sauté until they are tender and golden brown, approximately 5-7 minutes.

Once the mushrooms are sautéed, season them with salt and pepper to taste.

While the mushrooms are cooking, toast your bread slices until they are golden and crisp.

Place the sautéed mushrooms generously onto the toasted bread, distributing them evenly.

Top each open-faced sandwich with a generous handful of shredded Swiss cheese.

Place the sandwiches under a broiler until the cheese is melted and bubbly, about 2-3 minutes. Keep a close eye to prevent burning.

If desired, garnish with fresh herbs for a pop of color and freshness. Serve warm.