In a medium saucepan, whisk together the granulated sugar, cocoa powder, cornstarch, and salt.
Slowly pour in the milk while whisking constantly to create a smooth paste before adding the rest of the liquid. Place the saucepan over medium heat and cook, stirring frequently, until the mixture begins to bubble and thicken. Once it reaches a boil, reduce the heat to low and simmer for one minute while stirring to reach the perfect consistency.
Remove the pan from the heat and stir in the alcohol-free vanilla extract. Pour the warm pudding into six individual glass cups or small jars. Place a piece of plastic wrap directly onto the surface of the pudding to prevent a skin from forming, then refrigerate for at least two hours or until completely chilled.
In a cold bowl, beat the heavy whipping cream and powdered sugar together until stiff peaks form. Transfer the whipped cream into a piping bag fitted with a large round or star tip.
Once the pudding is set, pipe a thick circle of whipped cream around the top edge of each cup. Place a hulled strawberry, flat side down, in the center of the cream circle. Top the tip of each strawberry with a tiny dot of whipped cream and press a mini marshmallow on top to complete the hat.
