Slice the baguette into ¼” thick slices. Brush each slice with olive oil and season with salt and pepper. Toast using a grill pan or outdoor grill until both sides have visible grill marks, or bake in a preheated oven at 450°F (230°C) for about 7 minutes until golden and crispy. Set aside.

Heat 3-4 tablespoons of butter or olive oil in a hot skillet over medium-high heat. Add the sliced mushrooms, minced shallot, and fresh thyme leaves. Sauté for about 2 minutes until mushrooms begin to soften and shallots become fragrant.

Pour in ¼ cup of sherry vinegar to deglaze the pan, allowing it to simmer for about 30 seconds to reduce. Stir in 2 teaspoons of flour and cook for another 30 seconds while stirring constantly.

Gradually add ¼ cup vegetable stock (or broth or water) to the skillet, stirring to combine. Allow the mixture to simmer briefly until it thickens to a sauce-like consistency. Adjust seasoning with salt and pepper to taste. Remove thyme leaves if desired.

Spoon a couple of tablespoons of the mushroom mixture onto each toasted baguette slice. Garnish with additional fresh thyme leaves and a light drizzle of olive oil.