Preheat the oven to 375°F and line a baking sheet with parchment paper.
Mix the pumpkin puree, brown sugar, cinnamon, ginger, nutmeg, cloves, and cornstarch in a bowl until smooth.
Unroll the pie crusts on a lightly floured surface.
Cut each crust into rectangles, about 3 by 4 inches, for roughly six tarts total.
Spoon 1 to 1.5 tablespoons of filling onto half the rectangles, leaving a small border.
Brush egg wash around the edges of the filled rectangles.
Top with the remaining rectangles and press the edges together with a fork.
Poke a few small holes in the top of each tart to let steam escape.
Brush the tops with the remaining egg wash.
Bake for 20 to 24 minutes, until golden brown.
Cool completely on a wire rack before adding glaze, about 20 minutes.
Whisk the powdered sugar, milk, and vanilla together until smooth.
Spread the glaze over the cooled tarts and add sprinkles if you're using them.
Let the glaze set for about 10 minutes before serving.