Mix the old fashioned oats, brown sugar, cinnamon, and salt into a bowl. Add the vanilla extract and melted butter and stir to completely coat the oats and brown sugar in the melted butter.

Set aside while you make the pastry dough.

In a food processor, add the all purpose flour, ground cinnamon, salt, and cold cubed butter. Pulse on low until pea-sized clumps are formed.

While the processor is running on low, add the cold water 1 tablespoon at a time until a dough roughly forms.

Remove from the food processor and pour onto a work surface, using your hands to bring the dough together if it’s a bit crumbly. Flour the dough ball, the work surface, and a rolling pin.

Roll out to ⅛ inch thickness and then slice into 4 inch x 3 inch rectangles.

Fill half of the rectangles with the oatmeal filling and top with a 2 tablespoon of chocolate chips each. Add a second piece of dough to the top each each pastry.

Crimp the edges with a fork and use the tines of the fork to poke a few holes in the top. Slice any uneven edges of dough from the sides if desired.

Refrigerate for 1 hour until chilled through. Preheat the oven to 400°F.

Whisk the egg in a small bowl until the yolk is broken and mixed into the whites. Use a brush to brush the edges of each pastry with the egg wash.

Bake the pop tarts for 20 minutes, until the pastry is cooked through and golden brown on the edges.

Let cool on the pan for 5 minutes and then carefully transfer to a cooling rack to cool completely.

Add the powdered sugar, vanilla extract, milk, and cinnamon to a mixing bowl. Stir, using the back of your spoon to break up any clumps of powdered sugar, until a thick, but drizly consistency is reached.

Once the pop tarts are completely cooled, use a spoon to spread the frosting over the top of each pastry.

Let set slightly and then sprinkle with flaky sea salt, if desired. Store in an airtight container at room temperature for up to 4 days.