1. Melt butter in a 10-inch ovenproof frying pan over low heat. Remove from heat.
2. In a large bowl or blender, beat or whirl eggs until light and pale. Beat or blend in milk, vanilla, flour, sugar, and salt.
3. Pour batter into prepared pan and bake in a 425° oven until pancake is puffed and lightly browned, 15 to 20 minutes. Slice into wedges and serve immediately with raspberry sauce.
Raspberry sauce: In a food processor or blender, whirl 4 cups rinsed fresh or thawed frozen raspberries until smooth. Rub purée through a fine strainer into a bowl; discard seeds. Stir 1/4 cup sugar into raspberry purée; taste, and add more sugar if desired. Makes 1 1/4 cups.