In a medium saucepan, sift together the brown sugar, cornstarch, salt, and cocoa powder.
Gradually whisk in the milk until the mixture is smooth and lump-free.
Place the saucepan over medium to medium-low heat. Whisk constantly to prevent sticking or clumping.
Bring the mixture to a full boil, then reduce the heat to a simmer. Continue stirring and cooking for 1½ to 2 minutes, or until the pudding thickens.
Remove the saucepan from the heat and stir in the butter and vanilla extract until fully incorporated.
Pour the pudding into a bowl and press plastic wrap directly onto the surface to prevent a skin from forming.
Chill in the refrigerator for several hours for the best results.
Serve cold and enjoy!
