Mushrooms on Toast

Name: Mushrooms on Toast
Ingredients: 2 tablespoons butter; 1/2 pound mixed mushrooms, wiped clean with a damp cloth and thinly sliced; 1 tablespoon minced shallot; 1 pinch chopped fresh thyme (dried thyme substitutes just fine); 2 tablespoons dry sherry; 1/2 cup good chicken or vegetable stock (or if you're really good, which I'm generally not, you'll make some mushroom stock); 1/4 cup creme fraiche; 2 large eggs, cracked into two cups, yolks intact; 1 splash white vinegar; 2 thick slices of brioche; 2 teaspoons butter, melted; 1 teaspoon chopped chives; 1 teaspoon chopped chervil; sea salt and freshly ground black pepper