In a medium saucepan, whisk together the cornstarch, sugar, and salt. Gradually whisk in the whole milk until combined. Place the saucepan over medium heat, stirring constantly, until the mixture starts to thicken and bubble. This should take about 5-7 minutes.
Once the pudding has thickened, remove the saucepan from the heat. Add the coarsely chopped semi-sweet and bittersweet chocolates, stirring until completely melted and the mixture is smooth. Stir in the vanilla extract.
Pour the chocolate pudding into serving cups. Cover with plastic wrap, pressing it directly onto the surface of the pudding to prevent a skin from forming. Refrigerate for at least 2 hours, or until set.
In a mixing bowl, using an electric mixer, beat the cream cheese until smooth. Gradually add the heavy whipping cream and powdered sugar, mixing until soft peaks form. Then add the crème de menthe syrup, mint extract, and a few drops of green food paste. Mix until the color is evenly distributed and the cream is fluffy.
Once the chocolate pudding is set, remove it from the refrigerator. Top each pudding cup with a generous dollop of the mint grasshopper cream. Finish with bittersweet chocolate shavings for an elegant touch.