Creating the Mushroom and Fontina Tartine can be a delightful process if you follow these simple steps:

1. Preheat the Oven: Set your oven to 400°F (200°C) to prepare for baking the tartines.
2. Prepare the Bread: Slice the rustic bread into thick slices, about 1-inch each. Arrange them on a baking sheet.
3. Sauté the Mushrooms: In a large skillet, heat the olive oil and butter over medium heat. Add the minced garlic and sauté for about 30 seconds until fragrant.
4. Add Mushrooms: Toss in the sliced mushrooms and gently stir. Cook until the mushrooms are tender and golden brown, about 5-7 minutes.
5. Season: Season with salt and pepper to taste. If using fresh thyme, add it at this stage for added flavor.
6. Top the Bread: Spoon the sautéed mushrooms evenly onto each slice of bread.
7. Add Cheese: Sprinkle generous amounts of grated Fontina cheese over the mushrooms on each tartine.
8. Bake: Place the baking sheet in the preheated oven. Bake for about 10-15 minutes, or until the cheese is melted and bubbly, and the bread is golden brown.
9. Garnish and Serve: Remove the tartines from the oven. Garnish with freshly chopped parsley or additional thyme before serving.

These steps will guide you effortlessly through the process of creating this incredible tartine, turning a simple meal into something remarkably satisfying.