Prepare sausage gravy: In a skillet over medium heat, cook and crumble breakfast sausage until crispy. Stir in flour, then gradually whisk in milk until thickened. Season and set aside to cool.

Scramble the eggs: In a separate pan, scramble eggs on medium-low heat until desired doneness, about 4-5 minutes.

Make the pastry dough: Combine flour and salt, cut in butter and shortening until crumbly. Mix cold egg, vinegar, and water, then fold into flour mixture until a dough forms. Refrigerate for 30 minutes.

Roll and cut dough: Preheat oven to 375°F. Roll out dough to ⅛-inch thickness, cut into 3x4-inch rectangles.

Assemble Pop-Tarts: Line a baking sheet, place half rectangles. Brush edges with egg wash. Fill with sausage gravy and scrambled eggs, top with remaining rectangles and crimp edges.

Bake: Brush tops with egg wash and sprinkle cheese. Bake for 25 minutes until golden brown.

Cool: Let cool on baking sheet for 5 minutes before serving.