Dough
Filling
Glaze
In a food processor, pulse together flour, salt, sugar, and butter a few times, until the butter pieces are about the size of peas. Stream in the water, pulsing as you go.
Move the dough to a bowl or lightly floured surface and gently knead into a ball – be careful not to overwork the dough. Divide the dough in half, then wrap each half in plastic wrap and shape into a rectangle that's about ½" thick. Place the dough in the refrigerator to chill for 1-2 hours.
While the dough chills, mix together the brown sugar, cinnamon, flour, vanilla and melted butter until well combined and set aside.
Preheat oven to 300˚F and line a sheet pan with parchment paper.
Roll each half of the dough into a roughly 14 x 14" square on a floured surface. You should just barely be able to see the lines of your silpat or work surface through your dough, which should be about ⅛" thick. Make sure your surface is well floured, and sprinkle some flour on the dough before rolling.
Cut the dough into roughly 3.5 x 4.75" rectangles. You'll need to two for each pop tart. Combine your scrap dough and roll out again to minimize waste.
Spoon a little over a tablespoon of filling into each pop tart, then spread into a thin layer, leaving about ⅓" around the border. Beat an egg yolk and brush around the border of the filling. Dock the tops of your pop tarts with a skewer or a fork, then place over the bottom, and press down and then crimp the edges with a fork. Use a bench scraper to trim off any messy edges to get a perfect rectangle.
Bake for 25-30 minutes. They should be very lightly browned when you take them out, and the bottoms browned slightly. Let cool slightly before topping with glaze.
To make the glaze, add the butter, brown sugar and milk to a small saucepan over medium heat. Bring to a gentle simmer for 1-2 minutes, whisking until the brown sugar is dissolved. Remove from heat an immediately whisk in the vanilla, powdered sugar and cinnamon.
Immediately spread the glaze onto the pop tarts. It will harden up quickly. If you need to, put it back over medium-low heat to loosen it up again before spreading.
