In a small mixer bowl at low speed, beat milk, flour, eggs and salt until smooth. Cover and let stand at room temperature for 30 minutes.
Blend in melted butter. Heat a 7-inch skillet or crepe pan over medium-high heat; coat with butter. Immediately pour 2 tablespoons of the batter into skillet and quickly tilt skillet in all directions to spread evenly. Cook for about 1 minute on the first side; turn and cook about 30 seconds on the other. Place crepe on a plate; cover and keep warm. Continue with the remaining batter, brushing pan lightly with butter before frying each crepe.