To make the pastry, in a large mixing bowl, whisk together the flours, sugar, and salt. Add cold butter. Using a pastry cutter or two forks, cut the butter until it resembles coarse meal (pea-sized crumbles with a few larger pieces is ok). Slowly drizzle in the cold non-dairy milk 1 tbsp at a time, stirring with a wooden spoon or spatula after adding each tbsp. Stop adding milk once the mixture starts to clump. Form into a ball and flatten into a 1-inch thick disc. Tightly wrap in plastic wrap and refrigerate for 30 minutes.

While the dough is refrigerating, prepare the filling. In a mixing bowl, whisk together the brown sugar, cinnamon, melted butter, and maple syrup until a paste-like mixture forms. Set aside.

Take the dough out of the plastic wrap and cut in half. Wrap one half with plastic wrap and transfer to the fridge while you roll out the other.

Lay a sheet of parchment on to a flat surface. Place one of the dough balls in the center of it and lay another parchment on top of the dough ball. Using a rolling pin, roll the dough out into a 9x7" rectangle. Trim the sides as needed. Cut rectangle into fourths and transfer each smaller rectangle to a parchment-lined baking sheet. Transfer baking sheet to the fridge while you roll out the other dough ball.

Repeat step 4 with the other dough ball. Place baking sheet in the fridge for 10 minutes.

Remove 1 baking sheet of rectangles from the fridge. Place a heaping tbsp of the prepared brown sugar filling into the center of each rectangle, spread it around, leaving around 1/4 inch of space on the edges. Remove the other four rectangles from the fridge, these will be the tops of the pop tarts. Top each of filling-topped rectangles with a naked rectangle. Crimp the edges with a fork to seal. Pierce the surface of each pop tart. Brush each sealed pop tart with non-dairy milk. Sprinkle a bit of sugar over top.

Transfer filled and sealed pop tarts to the fridge to set for 20 minutes.

Preheat the oven to 350°F. Bake pop tarts for 25-30 minutes or until tops are golden brown. Cool for 5 minutes on the baking sheet then transfer to a wire cooling rack.

While pop tarts are cooling, prepare the icing. Whisk together all the icing ingredients until it reaches a spreading consistency. You don't want the icing to be too thick so that it's hard to spread. Spread icing on each pop tart using a knife. Icing will slightly harden within 30-45 minutes.

Store pop tarts in an airtight container at room temperature for up to 3 days or in the fridge for up to 5 days. To reheat, bake in a 350F oven for 10 minutes.