Preheat oven to 375 F. Place paper or foil baking cups in 30 -36 regular sized muffin cups.
Beat cake mix, cornstarch, vanilla & water in an extra large glass or metal bowl on low speed for 30 seconds then beat on medium speed for another 3 minutes. Fill cups 2/3-3/4 full of batter.
Bake 12 – 20 minutes or until golden brown & cracks feel dry. Remove from oven & cool completely.
Mousse Topping
Melt chocolate in a large microwave safe bowl for 30 seconds, then stir, heat for 30 seconds again, then stir well, then heat in 10 second increments, stirring between each, until smooth. Allow to cool 5 minutes.
Beat cream cheese in a large bowl with a hand mixer until smooth. Add chocolate & mix to combined, then mix in vanilla. Fold in the cool whip.
Spoon mousse into a pastry bag fitted with a large star tip. Make a generous swirl on top of each cupcake & decorate with some sliced strawberries. Refrigerate until served.