In a saucepan, combine sugar, cocoa powder, salt, and cornstarch. Mix well. Add in cold Horizon Organic milk, whisk until combined.
Increase heat to medium, stirring constantly until mixture reaches a boil.
Allow mixture to boil for 1 minute while stirring constantly. Remove from heat and stir in Horizon Organic butter and vanilla.
Allow mixture to cool completely, stirring occasionally to avoid a skin forming on the pudding.
Serve chilled or warm.
(Nutrition information provided is an estimate and will vary based on cooking methods and brands of ingredients used.)