Combine blueberries, lemon juice, cornstarch, and sugar in a small saucepan over medium heat. Bring mixture to a boil and then reduce to simmer for about 7 minutes, stirring frequently. 
Remove from heat and allow to cool completely. 

Preheat your oven to 425 degrees F. Line a large baking sheet with parchment paper. 
Cut each puff pastry sheet into six equally sized rectangles. (you will have 12 total)
Place 6 of the rectangles on the prepared cookie sheet and prick them with a fork so they don’t puff up. 

Add a spoonful of the blueberry mixture to the center, leaving a ½-1” border around the edges. 
Brush the edges with water, and place another rectangle on top to cover the blueberry mixture. Take care to line them up evenly. 

Press the edges down with the tines of a fork all the way around to seal the berry mixture inside. 
Pierce the tops with some holes with your fork.
Brush with egg wash.

Bake for 20 minutes, or until pastries are golden brown. 

Prepare the glaze by whisking all of the ingredients together in a small bowl. Add the cream a little at a time until you get your desired consistency. You want a thick, honey-like consistency. 

Cool the pastries for about 8-10 minutes before drizzling them with glaze.