For the cake:
1 (18 1/4 ounce) betty crocker white cake mix
1 1/4 cups water
1/3 cup oil
3 egg whites
For the filling:
8 ounces cream cheese
2 cups powdered sugar
3 tablespoons lemon juice
1 cup heavy whipping cream
For the crumb topping:
1/2 cup all-purpose flour
1/2 cup powdered sugar
1/4 cup cold butter
1/2 teaspoon vanilla extract
Make white cake following directions on box. Pour batter into 10-inch greased springform pan, and bake at 350 degrees for 40 - 45 minutes. Allow cake to cool completely when it comes out of the oven.
Make lemon cream filling by mixing cream cheese and powdered sugar in a medium bowl with an electric mixer until smooth. Mix in lemon juice.
Whip cream in a large bowl with an electric mixer on high speed until it forms stiff peaks. Combine cream cheese mixture whith whipped cream.
Make crumb topping by combining flour and powdered sugar in a medium bowl. Add butter and dribble in the vanilla extract. Use your hands to mix cold butter into flour and sugar. Break butter into smaller and smaller pieces as you incorporate it into the dry ingredients. Be sure not to press the mixture together. You want to end up with a very crumbly consistency with pieces no bigger than a pea.
When the cake is cool, slice it in half through the middle and remove the top. Spread all but 1/2 cup of the lemon cream mixture onto the bottom half of the cake, then carefully replace the top half of the cake.
Spread the remaining 1/2 cup of cream filling over the top and sides of the cake. Sprinkle the crumb topping on top of the cake and press it onto the sides all the way around the cake.
Chill the cake for at least 3 hours before your serve it.