Slice the baguette into ¼” thick slices. Brush each slice with olive oil and season with salt and pepper. Toast the slices by grilling on high heat until grill marks appear, or bake in a preheated oven at 450°F (230°C) for about 7 minutes until golden and crispy. Set aside.

Heat 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 soften and shallots become fragrant.

Pour in sherry vinegar to deglaze the pan, letting it simmer for about 30 seconds to reduce. Stir in flour and cook for another 30 seconds while stirring constantly.

Gradually add vegetable stock to the skillet, stirring to combine. Simmer briefly until the mixture thickens to a sauce-like consistency. Adjust seasoning with salt and pepper. 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 drizzle of olive oil.