1. Melt butter in small saucepan over low heat. Remove from heat; immediately stir in cocoa. Add sugar and evaporated milk.
2. Cook over low heat, stirring constantly, until mixture is smooth and hot. Remove from heat; stir in vanilla. Fondue will thicken slightly as it cools. Serve warm with Assorted Fondue Dippers. About 1-1/2 cups fondue.