Bacon-mushroom Frittata

Cut bacon into 1/2-inch pieces and separate with fingers. Finely slice greenonions or dice onion. Cut mushrooms into quarters. In 7- to 12-inch skillet, cook bacon on medium heat until slightly browned,about 4 minutes. Drain off half the fat. Add onion to bacon; cook untilsoftened, about 3 minutes. Add mushrooms and cook until browned, 3 minutesmore. Meanwhile, break eggs into bowl with milk or half-and-half. Whisk untilfrothy. Add vinegar, tarragon, salt and pepper. Whisk to combine. Gently pour eggs over ingredients in skillet. Reduce heat to medium and cookuntil edges begin to set, about 3 minutes, then cover. Cook until eggs havesolidified and puff a bit, about 4 to 5 minutes.