Next, add cubed unsalted cold butter into the bowl of food processor with the flour mixture. Pulse a little bit at a time until the flour mixture resembles coarse crumbs.

Slowly add in ice water a little a time until pie dough forms. 

Roll the dough out on a floured surface into a rectangle. The dough should be about a 1/4 inch thick. 

Cut the rectangle into strips approximately 3 inches wide and 8 inches tall using a pizza cutter or a knife.

Make the Filling: Mix together room temperature butter, brown sugar and cinnamon to make a paste. Note- melted butter will not work here as it will be too runny. 

The mixture should be spreadable but not thin like liquid. If it is too thin, add a little more brown sugar to get the right consistency. 

Fill the Pop Tarts: Remove the dough from the fridge and begin spreading the filling on half of each strip of dough leaving 1/2 inch space around the side to prevent oozing. Once the pop-tart is filled halfway up the strip, fold the remaining dough down to form a rectangle. Using your fingers, lightly press the edges closed all the way around. 

Then, take a fork and crimp the edges all the way around the dough ensuring the dough is well sealed. If you are having trouble getting the dough to stick, you can brush some egg wash around the inside edge of the dough before sealing. 

Pre-heat the oven to 350 degrees. While the oven is preheating, pop the poptarts in the refrigerator to chill the dough.

Brush the tops of the pop tarts with egg wash. Bake for 25-30 minutes at 350 degrees.

Make the icing: mix together brown sugar (or powdered sugar), cinnamon, vanilla and a splash of milk to make an icing to drizzle over the baked pop tarts.

Serve warm with icing.