Arrange and center oven racks, placing them one right under the other. Spray a 9 x 13" baking pan with non stick and set aside. Fill another baking dish half way up with hot water and place centered on the bottom centered oven rack Preheat oven to 325 degrees (F).
Place cream cheese blocks in a mixing bowl. Beat on high until smooth and creamy. Scrape bottom and sides of bowl and continue mixing on low speed. Add sugar, vanilla, lemon juice and lemon zest and continue mixing until well blended. Add egg yolks, one at a time, mixing well after each addition. After all yolks have been added, scrape bowl.
In a separate mixing bowl, beat egg whites until stiff peaks form. Scoop half of the egg whites into the cream cheese bowl and gently fold into the mixture. Add the remaining egg whites and repeat folding process.
Pour mixture in sprayed baking dish. Evenly smooth mixture with a spoon or spatula. Place on top centered oven rack and bake for 50-60 minutes. Carefully remove from oven and allow to cool completely. Once cooled, cover and refrigerate until needed.
Once ready for use, place cheesecake in a mixing bowl and whip until smooth and creamy. Transfer to a piping bag or sandwich bag and snip the bag or one of the corners.
Preheat oven to 350 degrees (F) and place liners in cupcake pan. Combine dry cake mix, flour, sugar and salt in a bowl and set aside.
In a large mixing bowl, combine egg whites, sour cream, vanilla, oil and champagne. Mix well. Slowly begin adding dry ingredients and continue mixing on low speed until well combined. Scrap bottom and sides of bowl and continue mixing for another 2-3 minutes.
Fill cupcake liners 2/3 full and bake for 20-22 minutes. Remove from oven and allow to cool 10 minutes then transfer to a baking rack to cool completely. Once cooled, use a teaspoon to remove some cake from the top of each cupcake, making a well for filling.
Beat cream cheese until smooth. Add butter and continue mixing until well combined and creamy. Add vanilla, salt and beat for another minute. With mixer on low, begin adding powdered sugar slowly. Stop and scrape bowl. Resume mixing on medium high until smooth and creamy. If mixture is too thick, add one tsp of milk (or champagne) at a time until desired consistency is obtained.
Transfer frosting to a piping bag that has been fitted with desired piping tip.
Pipe cheesecake filling into the well of the cupcake. Pipe frosting over cupcake, covering the cheesecake. Decorate as desired with sprinkles and/or melted chocolate. Top with Truffle or Chocolate Strawberry.
Refrigerate until ready to serve. Remove from refrigerator 30 minutes before serving.