For the Pop Tart Dough:

Combine the flour, cornstarch, confectioner’s sugar, salt, baking soda, and baking powder in a large bowl and whisk until combined.

Add the cold butter, and knead until it forms a sandy-looking mixture with some pea sized  pieces.

Pour in the cold cream and knead for 1 minute or until the mixture starts to come together into a  ball.

Pack the dough ball and shape into a rectangular flat disk and refrigerate for 30 minutes to an hour. 

For the Pumpkin Pie Spice Filling:

In a medium bowl, whisk together pumpkin, brown sugar, Pumpkin Pie Spice, cornstarch and salt until smooth. Transfer the mixture to a small saucepan and turn on medium heat. Stir continuously until the mixture starts to bubble for about 1 minute. Make sure to scrape the edges of your pan to prevent burning. Transfer the mixture to a bowl and cool in the fridge for about an hour. 

For the Pumpkin Spiced Pepitas:

Meanwhile the dough is chilling and the pie filling is cooling. Preheat the oven to 300°. 

Line a sheet pan with parchment and set aside.

In a small bowl, combine the nuts, sugar, agave, salt and Pumpkin Pie Spice.

Using your hands stir everything together until coated evenly.

Spread the coated seeds in an even single layer on the sheet pan and bake for 15-20 minutes, stirring occasionally to ensure an even toast.

Allow to cool completely and start sprinkling!

For the Assembly:

Preheat oven to 320°. Unwrap dough and cut in half. Re-wrap one half and return to the refrigerator. Roll out remaining dough on a lightly floured surface to about 14x10” rectangle. Transfer to a baking sheet lined with parchment paper.

Using a ruler, lightly score straight lines on dough to make a 3x3 grid (you should have 9 rectangles each measuring about 4½” long and 3¼” wide (don’t cut all the way through the pastry). Using the ruler, measure and lightly score another set of lines ¼” from the inside of each rectangle (think of it as making a slightly smaller rectangle inside each of the 9 rectangles. Chill dough until firm, 10–15 minutes.

Remove scored dough from the refrigerator and divide cooled filling among rectangles (about a slightly heaping tablespoonful each). Using a small offset spatula or a spoon, spread filling in an even layer so that it fills up to the lines of the smaller rectangles (you’re leaving the ¼” border exposed). Transfer to the refrigerator to chill. Roll out second piece of pastry into a 14x10” rectangle the same way as the first, then prick it all over evenly with a fork.

Crack egg into your hand, letting egg white fall into a medium bowl. Place egg yolk in a small bowl and beat to blend. Set egg white aside for making icing.Remove pastry with filling from the refrigerator and brush egg yolk over pastry, working around the filling. Drape the second piece of pastry over top, aligning the slabs and pressing out any air pockets. Press firmly around filling to seal pastry (take care to avoid the filling, though). Use a bench scraper to cut down between rectangles to make nine 4½x3¼” pop tarts; discard any scraps. Space pop tarts evenly on baking sheet. Chill until pastry is firm, 10–15 minutes.

Bake pop tarts until golden underneath and puffed but still pale on top, 30–35 minutes. Let cool on baking sheet.

For the Frosting: Add salt to reserved egg white and whisk until foamy. Add maple sugar and powdered sugar a little bit at a time, whisking constantly and vigorously until smooth and the icing with the whisk can form a  ribbon. Fill a disposable pastry bag or a resealable plastic bag with the icing and snip a very small opening from the end or a bottom corner. Pipe thin, even rectangles of icing on the surface of each pop tart, leaving about ¼-inch border. Working with 1 pop tart at a time, drizzle about 1-2 tablespoons of icing inside the icing rectangles. Using a small spatula cover the entire icing rectangle in a thin, even layer (add more icing if needed). Before the icing starts to set, top pop tarts generously with the candied pumpkin spiced pepitas. Let the pop tarts sit at room temperature at least 1 hour to let the icing dry before serving.