Preheat oven to 350 degrees F. Lightly grease a (13"x18") rimmed half sheet baking pan with non-stick spray and set aside.
For the Crust:
Cream together butter and sugar in the bowl of a stand mixer fitted with a paddle attachment. Add the eggs one at a time, beating well after each egg. Add in vanilla.
In a separate bowl combine the flour, salt, and baking powder. Gradually add the dry ingredients to the wet and mix until a soft dough forms. Reserve 1 heaping cup of the dough and press the remaining dough evenly into the prepared pan.
For the Filling:
In a clean bowl, beat the cream cheese, egg, ½ cup sugar, and vanilla together until smooth and creamy. Spread over the top of the dough in an even layer. Top with the mashed peaches and drop remaining dough over the filling in small pieces.
Bake for 30-35 minutes, until toothpick inserted in center comes out clean. The center might be slightly jiggly still, but this is ok. Let the bars cool completely.
For the Icing:
Combine the icing ingredients in a bowl and whisk until smooth. Add more powdered sugar for thicker consistency, or more cream for smoother consistency. Drizzle over the cooled bars, slice and enjoy!
Notes
*Substitute peaches for raspberries, blueberries or strawberries if desired!