In a standing mixer or large bowl cream together butter and sour cream until smooth.
Slowly add in the powdered sugar until completely incorporated.
Pour in 1 TBSP at a time of milk until consistency is about the same as thick cake batter.
Evenly spread frosting over sugar cookie crust.
Slice strawberries into 3-4 slices, depending on the size of the strawberry.
Starting on the long edge of the pizza, layer the sliced of strawberry making sure they are all in the same direction.
Do the same along the opposite side.
Evenly space out two more strips of sliced strawberries in between the two lines on the outside crust.
Fill in between the strawberry rows with blueberries.
Chill in the refrigerator for 30 minutes before cutting into 30 squares.
This can be chilled for up to 2 days before serving. Cover with plastic wrap if you chill it longer than 30 minutes.