Add flour, Whisps, cornstarch, salt, and sugar into food processor. Pulse ingredients a couple of times, just to combine the ingredients.

Add cubes of butter to your dry mixture and pulse about 1-2 times. Small bits of butter should still be visible in your dough.

Add egg and pulse 2-3 times, or until egg is fully incorporated.

Add a tablespoon of water at a time, pulsing mixture between each addition until you have a soft dough.

Remove dough from food processor and shape it into a round disc. Cover it in plastic wrap and let it chill in your fridge for about 45 minutes to an hour.

Get a medium saucepan and place your blackberries, sugar, cornstarch, and lemon juice in it. Mix the ingredients, ensuring the dry ingredients are covering your berries.

Place saucepan with your berry mixture on your stovetop on medium heat. Stir occasionally.

Let berries break down a bit until the mixture begins bubbling. Add thyme.

Stir constantly until the mixture thickens. The mixture will be ready when it coats and sticks to a spoon.

Remove from heat. Let mixture fully cool and place in an airtight container.

Preheat your oven to 350F and set aside two baking sheets lined with parchment paper.

Take dough out of fridge. Place your disc of dough between two pieces of parchment paper or a clean and lightly floured surface.

Roll dough about 1/4 of an inch thick and trim edges to get a rectangle. Cut into smaller rectangles that are 4 inches long and 2 ½ inches wide. Re-roll and cut as needed to get 12 rectangles.

Combine an egg and milk into a small bowl to make egg wash.

Place three pastry rectangles on each baking sheet. Brush egg wash around the edges of each rectangle.

Place about 1 ½ to 2 tbsp of jam in the middle of each pastry.

Place one of your remaining six pastry rectangles on the top of your prepared one, lightly pressing it to seal the tarts together.

Using a fork, crimp the edges of each tart and brush each tart with egg wash.

Place both baking sheets in oven for 25 to 30 minutes, until your pop tarts are golden brown.

Let each tart completely cool.

While tarts are cooling, prepare icing by placing powdered sugar, milk, and vanilla into a large bowl.

Using an electric mixer, mix all ingredients until a very thick icing is formed. (Add extra milk if necessary, but the ideal icing is quite thick).

Add tablespoon of jam and mix until fully incorporated.

Spoon or drizzle desired amount of icing onto each cooled tart. Let icing harden.

Enjoy your pop tarts!