If using shiitakes, remove the stems. Slice all the mushrooms. In a medium frying pan, heat 2 tablespoons of the butter over moderate heat. Add the sliced mushrooms and cook, stirring occasionally, until they begin to brown, about 5 minutes. Add the garlic, the remaining 1/2 teaspoon salt and a pinch of pepper and cook 1 minute longer. Stir in the tomato and cover to keep warm.