Preheat oven to 350 degrees. Lightly butter a 9" square baking pan. Toast bread until lightly crisp. In a med. saucepan combine milk, chocolate chops, and butter. Cook over low heat stirring until chocolate is melted. Tear bread into large pieces (5-6 pcs. per slice). Scatter bread evenly in baking dish. In med. bowl, whisk eggs, sugar and vanilla. Whisk in warm milk mix until combined. Pour over bread. Bake until pudding has puffed up and is firm, or about 25 min. Cool at least 10 min. and dust with powdered sugar before serving.