Preheat oven to 300 degrees F. Spray a shallow soufflé dish with vegetable spray.
In saucepan, combine sweetened condensed milk and chocolate, cook over low heat stirring constantly until chocolate is melted. Add butter; stir until melted. Remove from heat; whisk in milk, egg yolks, vanilla and rice.
Pour into prepared baking dish. Cover loosely and bake for 30 to 40 minutes. Cool on wire rack. Refrigerate until chilled.