½ ounce dried porcini mushrooms
1 cup chicken stock
1 thick Parmesan rind
3 tablespoons butter
1 small shallot, minced (about ¼ cup)
1½ pounds mixed mushrooms, sliced
1 tablespoon sherry vinegar
2 tablespoons chopped tarragon
Salt and freshly ground pepper
6 thick slices crusty bread, toasted
¼ cup extra-virgin olive oil
6 poached eggs
1. In a small, heatproof mixing bowl, pour 1 cup of boiling water over the dried porcinis and let soak until softened, about 15 minutes. Meanwhile, in a medium saucepan, bring the chicken stock to a simmer over medium heat and add the Parmesan rind. Reduce the heat to low, cover and simmer gently.
2. Drain the porcinis, straining and reserving the soaking liquid. Coarsely chop the porcinis and set aside. Add the soaking liquid to the simmering chicken stock and simmer gently.
3. Meanwhile, in a large, deep skillet, melt the butter over medium-high heat. Add the shallot and cook until softened, about 3 minutes. Add the mushrooms and reserved porcinis and cook, stirring occasionally, until the mushrooms have begun to brown, about 15 minutes.
4. Remove and discard the Parmesan rind from the saucepan and add the chicken-mushroom stock to the skillet. Bring the mixture to a boil over medium-high heat simmer, stirring frequently, until the liquid has reduced by one-third, about 10 minutes longer. Remove the skillet from the heat, stir in the sherry vinegar and tarragon and season to taste with salt and pepper.
5. Arrange the toasted bread on a platter and drizzle with the olive oil. Spoon the mushrooms over the bread and top each portion with a poached egg. Season with salt and pepper and serve immediately.