Start with the filling and placing all the ingredients into a pot over medium heat. Stir occasionally. Cook for 6-8 minutes, the mixture should thicken and the strawberries and rhubarb should be soft. Use an immersion blender or you could use a potato masher to puree the mixture. I like to leave a few small chunks. Transfer to a bowl and chill until ready to use. *You will have extra left over, reserve this for the glaze as well as future use!
Make the dough placing all the ingredients (except the water) into a food processor and pulsing until combined. Add 2 tablespoons of cold water and pulse just until the dough starts to come together. Resist the urge to add more water or this will result in a less flaky dough. Pack the dough together into a disc and then place it between two pieces of parchment paper. Roll the dough out until it's roughly 1/8 " in thickness and use a 2" round cookie cutter to cut out as many circles as you can. Repeat until you have used all the dough.
Place half of the circles onto a baking sheet lined with parchment paper about 1-2 inches apart. Spoon about 1 tablespoon of strawberry-rhubarb filling into the center. Cut 4 small slits into the raiming cutouts and place them over the filling. Use a fork to press the edges together. Whisk together the egg wash and brush it over the pop tarts. Bake the pop tarts for 24-27 minutes and the edges are golden brown at 350 F. Let cool.
Whisk together the about 1 tablespoon of the remaining strawberry rhubarb filling, almond milk and powdered sugar until smooth and pourable but thick consistency. Add more almond milk if needed.
Notes
Store the pop tarts in an airtight container and refrigerate for up to 5 days.