Start your pop tart dough. Get a medium-sized bowl and whisk your flour, salt, and sugar until well combined. Then cut your cold vegan butter into small squares and add it to the flour mixture, then add your shortening, and use a pastry cutter or two forks until the dough has coarse crumbs. Last, add your cold vegan milk and fold with a wooden spoon until it's combined well. Wrap this in a saran wrap disc and place it in the fridge while you prep the rest of the ingredients.
Preheat your oven to 350 degrees, line a cookie sheet with a Silpat or oven-safe parchment paper, and set it aside.
Get a small to medium bowl and combine your brown sugar middle. Melt the vegan butter in the bowl, add the brown sugar, flour, and cinnamon, and stir until well combined.
After about 20-30 minutes, your dough should be ready to roll. Grab two large sheets of parchment paper (enough to cover the top and bottom of the dough you're going to use to roll out the dough. Place one sheet on the bottom and place your dough disc in the middle, then place the other piece of parchment paper on top of the dough, get your rolling pin and roll out the dough into a rectangle until it's about ⅛-1/4 inches thick, then take a pizza cutter and square up your dough. That means cutting off the jagged areas and making them even rectangles. If you have a rectangle cookie cutter, you can use that or grab a ruler and measure the height, then divide it by how many even pieces you want and make little score marks so you know where to cut and do the same thing up and down. You should have an exact number of squares to make the tarts. If you're like me and don't roll out very well, you will need to re-roll the excess dough just like you did before.
Get a small bowl or cup and add the vegan egg wash 1 TB maple syrup with 1 TB soy milk and stir until combined. Brush this on what will be the bottom of the tarts, just a light coat, then add about 1 ½ TB of brown sugar mixture onto the tarts, leaving a rim around the edge of the tart with no brown sugar. Then place your top onto the brown sugar-covered bottom tart. Take a fork and seal the edges of the tarts by crimping them. Last, cover them with the vegan egg wash lighting and poke a hole gently three times with the fork to vent the tart.
Bake in the preheated oven for 16-22 minutes until lightly golden and cooked through. Let cool on the cookie sheet for 5 minutes, then use a spatula and place them on a cooling rack.
While the tarts are cooling, you can make the icing. Take a small bowl and combine the frosting ingredients with a whisk until smooth if it's too thick, add only a tiny bit more plant milk; if it's too thin, add a little more powdered sugar. Let the tarts cool completely before frosting. I used a spoon and just smoothed it over where I wanted it.
Store in an airtight container on the counter for up to 4 days.