In a large bowl, whisk together the flour, baking powder, baking soda, and sugar.

Add in the cold and grated butter, and mix with a wooden spoon to coat.

Then add in the greek yogurt, sourdough discard, heavy cream, and vanilla. Mix until the mixture comes together and a dough ball has formed, you may need to use your hands to really get it to form!

Lay the dough on a floured surface. Using your hands, fold the dough over itself 3-4 times, and shape it into a 1” thick rectangle or circle. Wrap the dough in plastic wrap and let sit in the fridge for at least 30 minutes.

Preheat oven to 400F. Line two baking sheets with parchment paper, and set aside.

Once the dough has rested, flour a work surface to roll the dough out, you can also do this on a piece of floured parchment paper. Roll the dough into a large rectangle (36”x8”), about ⅛” thick. Feel free to split the dough into 2 different pieces to roll out if your surface isn’t large enough.

Using a pastry cutter, or knife, cut the dough into rectangles about 2” wide x 3” in height. You should get 20-24 rectangles, depending on how thick the dough was rolled out!

Take half of the rectangles and place them onto the prepared baking sheets (these will act as the bottoms).

Brush the edges of each bottom rectangle with the egg wash. Fill each center with 1 heaping teaspoon of blueberry jam, leaving a ¼” border around the edges. Cover each bottom piece with the filling with a second dough rectangle on top. Use your fingers to slightly press down around the edges. Then, use a fork to press and crimp the edges.

Repeat the process with the remaining dough rectangles and filling.

Brush the tops of the pop tarts with the egg wash. Bake at 400F for 13-15 minutes, or until crisp and golden brown.

While the pop tarts are baking, make the glaze by whisking together all of the ingredients in a medium bowl, until smooth.

Once the pop tarts are cooled, top with the glaze and serve.