Preheat oven to 375°F. Line a large baking sheet with parchment paper. Roll 1 pie crust into a 12- x- 8-inch rectangle. Carefully place rectangle on prepared baking sheet.
Spread preserves in an even layer on dough, leaving a 1-inch border on all sides. Combine egg and water in a small bowl. Carefully brush egg mixture on border.
Roll second pie crust into a 12- x- 8-inch rectangle; place over first crust, covering preserves completely.
Using a fork, gently crimp all edges of pastry, and poke a few holes in top to release air; brush top of pastry with egg mixture. Bake 15 minutes or until golden brown.
Meanwhile, whisk sugar, cream, vanilla, salt, and, if desired, food coloring in a large bowl. Add additional cream, 1 Tbsp at a time, if desired, to reach desirable consistency.
Allow pastry to cool completely; spoon prepared glaze over pastry. Top with sprinkles, if desired.