In a large bowl, whisk together flour, cocoa powder, sugar, and salt.

Add cubed butter to flour mixture and cut the butter in until the mixture resembles fine crumbs.

In a separate medium bowl, stir together egg, buttermilk, vinegar, and red food coloring.

Add wet ingredients to the bowl with dry ingredients and combine until the dough comes together. Knead gently in the bowl.

Divide dough into two equal-sized balls, wrap each with plastic wrap, press gently into discs, and refrigerate for about an hour.

Preheat oven to 375 degrees and line two large baking sheets with parchment paper.

On a lightly floured surface, roll one of your pastry discs out until it's about ⅛" thick. Use a cookie cutter to cut out hearts and set cut-outs on the prepared baking sheet. Re-roll dough and continue to cut. Repeat with the second portion of dough.

Brush the edges of the dough with a little buttermilk and add a small scoop of cream cheese filling onto half of the hearts.

Place a second dough heart on top of the cream cheese topped ones and press down around the seams to seal them tight.

Press the tines of a fork around the edges and prick the tops multiple times to allow steam to escape. Brush the tops of the Pop Tarts with more buttermilk.

Bake for about 20-24 minutes, until the tarts are cooked through and getting crispy. Remove and cool on metal racks.

Top each of the cooled Pop Tarts with icing and add sprinkles.