Heat oven to 400 degrees F. Spray a large baking sheet with no-stick cooking spray. Chill beaters from electric mixer and medium mixing bowl for 10 minutes in the freezer. Combine muffin mix and 2/3 cup cream in medium bowl. Stir with a fork until all ingredients are moistened and mixture forms a dough. Press into a ball. Pat into a 7-inch round on lightly floured surface. Cut into 8 wedges. Place on baking sheet. Bake 12 to 15 minutes or until golden brown.
Beat cream and vanilla in chilled bowl, gradually adding powdered sugar on medium speed until cream begins to thicken and stiffen.
Split shortcakes; fill with strawberries and top with whipped cream and additional strawberries.