In a large skillet over medium-high heat, brown the breakfast sausage for 5-7 minutes until it's golden and fully cooked. Sprinkle in a few tablespoons of flour, stirring well to combine, then gradually add in the milk while whisking continuously. Keep cooking until the mixture thickens and bubbles, seasoning with salt to enhance the flavor of your sausage gravy.

In a separate pan, crack open your eggs and scramble them over medium heat. Stir gently just until they’re set but still soft, around 3-4 minutes. This texture is critical to prevent sogginess in your Savory Breakfast Pop-Tarts. Once done, remove from heat and set the scrambled eggs aside to cool slightly before filling your pastries.

In a mixing bowl, combine all-purpose flour and salt, then cut in the cold vegetable shortening and butter using a pastry cutter or fork until the mixture resembles coarse crumbs. In a small bowl, whisk an egg with vinegar and cold water, then gradually mix this into the flour until just combined. This dough will create the flaky crust for your pop-tarts.

On a lightly floured surface, roll out the dough to about 1/8-inch thickness. Using a sharp knife or pastry cutter, cut the dough into 3 x 4-inch rectangles, ensuring you have an equal number of tops and bottoms. Place half of these rectangles onto a lined baking sheet, ready for filling.

With a pastry brush, lightly brush the edges of the rectangles on the baking sheet with egg wash to help seal your pop-tarts. Spoon a generous amount of the scrambled eggs and creamy sausage gravy onto the center of each rectangle. Top with another rectangle of dough, pressing down the edges and using a fork to crimp for a secure seal.

Preheat your oven to 375°F (190°C). Once the pop-tarts are assembled, brush the tops with egg wash to achieve a beautiful golden color while baking. If desired, sprinkle some jack cheese on top for added flavor. Bake for 25 minutes or until the pop-tarts are golden brown and flaky.

After baking, let the Savory Breakfast Pop-Tarts cool on the baking sheet for about 5 minutes. Transfer them to a wire rack to cool completely before serving. Enjoy warm or at room temperature.