For the pastries

1 1/2 cups all purpose flour

1/2 cup unsalted butter, cold and cubed

1 teaspoon sugar

1 pinch salt

1 cold egg, beaten

1 tablespoon cold water (optional)

8 tablespoons jam or preserves

2 tablespoons milk or beaten egg, for brushing the top of the pop tarts

For the topping:

1 cup powdered sugar

2 teaspoons hot water or milk

Sprinkles, to decorate