In a large bowl, combine flour, sugar, baking powder, salt, and butter.

Use your fingers or a fork to work the butter into the dry ingredients until the butter pieces are about the size of a pea.

Add in 6 tablespoons of water and mix until it starts balling together into a dough.

Divide the dough in half and shape each half into a rough disk shape. Wrap each disk with plastic wrap and chill in the fridge for 1 hour.

In a medium bowl, mix together brown sugar, flour, and cinnamon to combine.

Take 1 of the chilled disks of dough out of the fridge and place on a lightly floured work surface.

Use a rolling pin to roll the dough out into a roughly 9x14 inch rectangle.

Trim off any rough edges to create a neater rectangle then carefully lift the dough up and onto the parchment lined baking sheet.

Place the baking sheet into the fridge while you work on the second dough.

Take the second disk of dough out of the fridge and place onto a lightly floured work surface.

Lightly knead the dough to warm it up, then roll this dough out into the same size as the first one and trim off any rough edges.

Use a fork to poke holes into the top of this dough to help steam escape as the pop tart bakes.

Take the baking sheet with the first dough out of the fridge and sprinkle the pop tart filling evenly on top of the dough leaving a roughly 1 inch border along the edges.

Dip your finger or a brush into water and lightly wet the exposed edges of the dough.

Lay the second rectangle of dough on top and use a lightly floured fork to press the edges together to seal.

Transfer the pop tart to your freezer for at least 10 minutes or however long it takes to preheat your oven.

In a small bowl, whisk together the egg and milk for the egg wash.

Take the chilled pop tart out of the freezer and brush the egg wash on top.

Bake the giant pop tart in the center of your preheated oven for 25 to 30 minutes or until golden brown on top.

Cool the pop tart completely to room temperature before icing.

In a medium bowl, whisk together powdered sugar, cinnamon, and 1 tablespoon of water until smooth and pourable.

Pour the icing over the cooled pop tart and spread evenly on top.

Let the pop tart sit out for about 20 to 30 minutes to allow the icing to dry and set for cleaner slices.

Slice and serve plain or with a sprinkling of sea salt.