Working one sheet at a time, roll out the pie crusts to about a 1/8" thickness and cut into 3" x 4" rectangles. You should get 6 rectangles out of each dough roll.
Place 12 of the dough rectangles onto baking sheets. These will be the bottoms of the tarts.
Beat the egg with 1 tablespoon water and brush onto the crusts.
Make the filling by combining all ingredients and place 1 heaping tablespoon onto the center of each tart bottom. Do not get the filing within 1/4" of the edges of the dough.
Place the remaining dough rectangles on top of the bottoms and press down along the edges with your fingers to seal.
Use a fork to then crimp the edges.
Brush tops with egg wash.
Bake 20-25 minutes or until golden brown.
Remove from oven and let cool completely.
Make the icing by combining all the of ingredients, beating with a fork. Add more milk if the mixture is too thick, but don't add too much or it'll be too thin.
Brush icing on top of tarts.
Serve hot.
Notes
You can freeze these and drop them in the toaster or toaster oven to reheat.