Pre-heat oven to 350.
In bowl prepare cake mix according to package directions.
Grease 2 9" round cake pans and add your cake batter.
Cook for time stated on back fo 9" pans.
Meanwhile to make the filling/frosting, in bowl beat your cream cheese until creamy, add in your powdered sugar 1 cup at a time then add your lemon juice and beat until blended.
In separate bowl beat your heavy whipping cream until stiff peaks form and gently fold into the cream cheese mixture, refrigerate until ready to use.
Remove cakes from oven and set aside to cool completely.
Once completely place one of your cake layers on a cake stand or turntable and spread with 1/3-1/2 of your filling/frosting mixture.
Top with other cake round and then frost top and sides with remaining frosting.
Place in your refrigerator for about 1 1/2-2 hours.
To make crumb topping, in bowl add your flour, powdered sugar and vanilla and stir until blended.
Add in your butter and with pastry cutter or hands, crumble mixture until crumbs form.
Take cake out of refrigerator and sprinkle top with crumbs and press up the sides, place back in refrigerator and allow to chill another 1 1/2 hours before serving.