Cut the unsalted butter into smaller pieces and mix the other dough ingredients in a mixer or by hand until they form a ball. Put it in the fridge while you get the filling ready.
Chop the apples into small squares and cook them with the other filling ingredients in a small pot, stirring occasionally for about 10-15 minutes. Let it cool.
While the filling is cooling, mix the frosting ingredients until smooth and set aside.
Puree the apple mixture in a food processor or blender.
Preheat the oven to 350°F (200°C). Roll out the cooled dough to form a big rectangle, then cut it into 12 smaller rectangles.
Put about two tablespoons of apple filling on six of the rectangles, spreading it but not all the way to the edges.
Cover those six rectangles with the remaining six, with a small fork, press around the edges and gently, pierce about three times on top.
Brush the pop tarts with almond milk or your preferred milk, then bake them for about 20-24 minutes.
Let the pop tarts cool for at least 15 minutes, then add the frosting, sprinkle a little more cinnamon powder, and enjoy!
