Preheat oven to 425˚F
Melt butter in a medium skillet over medium heat.
Add onions and sugar and stir together. Cook mixture until onions are lightly caramelized, but still have body to them, 8 to 10 minutes. Season with salt and pepper. Remove from heat and allow onions to cool, about 15 minutes.
Combine pulled pork, barbecue sauce, shredded cheese, onions, and pepper into a large mixing bowl and completely mix together. Set aside.
To assemble: Roll chilled dough out onto a lightly floured surface into a 18” x 27” rectangle.
Cut out 3, 6”x 9” rectangles and brush the surface of each with the beaten egg. place ⅓ cup of the filling mixture into the bottom half of each rectangle (leaving a ¼ inch border).
Fold the top half of the rectangle-cut dough over the filling and gently press around the edges, getting rid of any air pockets. Using the back of a fork, seal the open edges. Gently score the top of each pop tart and brush with egg wash. Place them onto a parchment lined baking sheet, 1 inch apart and place in the freezer.
Repeat steps 5-7 with the remaining dough and filling.
Allow pop tarts to freeze for about 15-20 minutes, before baking in the oven for 20 to 25 minutes or until the pop tarts are golden brown.
Allow pop tarts to cool, about 10 minutes, before serving.