Melt butter in a 10-inch ovenproof frying pan over low heat. Remove from heat.
In a large bowl or blender, beat or whirl eggs until light and pale. Beat or blend in milk, vanilla, flour, sugar, and salt.
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.