In a large bowl, combine flour, sugar, baking powder, salt, and butter. - 2 ½ cups (300g) all-purpose flour, 1 tablespoon granulated sugar, ½ teaspoon baking powder, ½ teaspoon salt, 1 cup (225g) unsalted butter

Use your fingers or a fork to work the butter into the dry ingredients until you have a coarse and crumbly mixture with the butter pieces about the size of a pea. Try to work relatively quickly to keep the butter as cold as possible (colder butter = flakier crust!)

Add 6 tablespoons of water and mix it into the dry ingredients until it starts balling together into a dough. - 6 to 8 tablespoons ice cold water

If you squeeze some of the mixture with your fingers, it should stick and shouldn't crumble but it shouldn't be sticky. If it's too dry, continue mixing in cold water, 1 tablespoon at a time, until it comes together.

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

In a medium bowl, mix together brown sugar, flour, and cinnamon until evenly combined. - ⅔ cup (130g) light or dark brown sugar, 1 tablespoon all-purpose flour, 2 teaspoons ground cinnamon

Back to the chilled dough, take 1 of the disks of dough out of the fridge and place on a lightly floured work surface. To make it easier to roll without cracking, you can let the dough sit for 10 to 15 minutes at room temperature to soften slightly or lightly knead it with your hands to warm it up a bit.

Roll the dough out into a roughly 9x14 inch rectangle. Add flour as needed to keep the dough from sticking.

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. 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 it bakes.

Now back to the first dough that's sitting in the fridge, take the baking sheet out and sprinkle the cinnamon sugar 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 about 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. - 1 large egg + 1 tablespoon milk

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. If the icing is too thick, add a splash more water until it reaches your desired consistency. - 1 cup (130g) powdered sugar, ½ teaspoon ground cinnamon, 1 to 2 tablespoons cool water

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. Don't sprinkle the sea salt on the icing while it's still wet or it can draw out water and keep it from setting.