Allow the pie crusts to defrost on the counter for about 20 minutes. Preheat the oven to 350F. Line a baking sheet with a silicone baking mat or parchment paper.
Remove the defrosted pie crusts from the tin and carefully place them on the counter. Use a rolling pin to gently flatten them out (but don't roll them thinner).
Using a heart shaped cookie cutter, cut 10 hearts out of each pie crust.
Place half the hearts on the silicone baking mat. Set the other half aside.
Add a generous spoonful of blueberry jam to the middle of each heart.
Beat the egg and add a small splash of water to it. Using your finger (or a small brush), spread the egg around the edges of the pie heart shape so that it completely covers all of the exposed crust around the jam.
Place another heart over top of the jam and gently press down with your fingers to line it up and start sealing it.
Press down around the edges of the heart shape with a fork to seal it all in.
Brush the egg mixture on top of each of the hearts. It helps give them that wonderful golden brown colour while they're baking.
Then bake at 350F for 20 to 30 minutes until they're golden brown. Mine were done at about 23 minutes so keep an eye on them after 20 minutes.
For the glaze:
Add the icing sugar to a bowl, and slowly stir in the milk until it's a smooth, slightly runny consistency.
Drizzle the glaze over the heart shaped pies while they are still warm.