For Cake: Preheat oven to 350 F. In a bowl, mix the butter and cake mix, then mix in 1 egg. Press into an ungreased 9x13 pan.
In a separate bowl, beat second egg and cream cheese. Add powdered sugar (a couple big spoonfuls at a time), vanilla and salt. Mix well and pour into cake pan. Bake 30-35 minutes. Make the topping below.
For Topping: Pour about a cup of the Cherries in Syrup from the jar into a saucepan and add the sugar and the lemon juice. Reduce over medium heat to about ¼ cup (takes about 20 minutes).
Mix in the cornstarch and water. Whisk into the syrup and bring back to a boil for about a minute. Add back about 1 and ¼ cup of cherries from the jar. Let cool before spooning over individual slices of cake. This topping is great on ice cream and cheesecake, too.