1-In a food processor, combine the flour,: In a food processor, combine the flour, butter, sugar and salt and pulse a few times until the butter pieces are pea-sized. Stream in the cold water, pulsing as you go, until a crumbly dough forms.
2-Transfer the dough to a lightly floured: Transfer the dough to a lightly floured surface and gently knead it into a ball. Divide the dough in half and wrap each half in plastic wrap, flattening each one into a rectangle that’s about 1 inch thick. Refrigerate for 1-2 hours.
3-To make the filling, add the blueberries,: To make the filling, add the blueberries, honey, lemon juice and lemon zest to a saucepan over medium heat. Gently smash the blueberries, then reduce the heat to medium-low and simmer for 20-25 minutes, stirring and mashing occasionally, until the mixture thickens. Remove from heat and cool completely.
4-In a small bowl, reserve 2 tablespoon: In a small bowl, reserve 2 tablespoon of the filling for the glaze and set aside.
5-Preheat the oven to 300˚F (150˚C) and: Preheat the oven to 300˚F (150˚C) and line a sheet pan with parchment paper.
6-On a well-floured surface, roll one half: On a well-floured surface, roll one half of the dough into a large rectangle about ⅛-inch thick, then trim it into a straight-edged rectangle that’s 14×10 inches. Cut the rectangle in half lengthwise, then cut each half into 4 rectangles for 8 total rectangles.
7-Repeat with the other half of the: Repeat with the other half of the dough. In total, you will have 16 rectangles of the same size.
8-Using a fork, dock several holes in: Using a fork, dock several holes in the center of 8 of the rectangles (these will be the tops). Into the centers of the other 8 rectangles, spoon about 1 ½ tablespoon of the filling and spread into a thin layer, leaving a border around the edges.
9-Around the border of the filling, brush: Around the border of the filling, brush the beaten egg yolk, then place one of the docked rectangles on top, pressing down the edges to secure. Using the tines of a fork, crimp and seal the edges of each tart. Transfer to the sheet pan, then repeat with the remaining pop tarts.
10-Bake the tarts for 30-35 minutes, until: Bake the tarts for 30-35 minutes, until very lightly browned on the top and edges and golden brown on the bottom. Carefully transfer to a cooling rack to cool completely.
11-To make the glaze, add the reserved: To make the glaze, add the reserved 2 tablespoon blueberry filling to a small bowl with 1 tablespoon water and stir to combine, then strain it through a fine mesh sieve into another bowl, extracting as much blueberry juice as possible.
12-Add the powdered sugar and lemon juice: Add the powdered sugar and lemon juice to the blueberry juice and whisk until smooth. Spread as much of the glaze as you’d like over the cooled tarts and top with sprinkles.