Soak the porcini mushrooms with 1 cup water in a bowl; cover and let stand for 15 minutes or until softened. Drain the mushrooms in a fine sieve over a bowl, reserving liquid.
Put oil and garlic in a large skillet over medium-high heat; sauté until garlic sizzles. Add porcinis, reserved mushroom liquid, and parsley; cook until the liquid evaporates. Add the button mushrooms, salt, and pepper; cook for 15 minutes or until the liquid has evaporated.