For the pastry crust:
2 cups all-purpose flour
1 tablespoon granulated sugar
1 teaspoon salt
1 cup (2 sticks, or 8 ounces) unsalted butter, cold and cubed
2 tablespoons milk
For the cinnamon sugar filling:
½ cup light brown sugar
1½ teaspoon ground cinnamon
4 teaspoons all-purpose flour
For the strawberry filling:
¾ cup strawberry jam (or whatever flavor you'd like)
1 tablespoon cornstarch
1 tablespoon water
1 egg, lightly beaten (to brush on pastry)
1. Prepare the cinnamon sugar filling by whisking the ingredients together.
2. If using the strawberry filling, prepare by whisking together the cornstarch and water, and then combine with the jam in a small saucepan. Bring to a boil and simmer for 2 minutes, stirring frequently. Remove from the heat and let cool.
3. To make the crust, whisk together the flour, sugar, and salt. Using your fingers or a pastry blender, work in the butter until it is the size of peas and the mixture holds together when you squeeze it. Whisk together the egg and milk and add to the dough. Mix together with a fork until everything is evenly moistened. Knead briefly on a floured surface, if necessary, until the dough comes together.
4. Divide the dough in half. (At this point you can wrap each in plastic wrap and refrigerate for up to 2 days.) If you refrigerate the dough, let it come to room temperature for about 15 minutes before rolling out. Roll out one piece of dough to about 1/8-inch thick, in a 9½ by 12½ rectangle. Using a sharp knife, pastry wheel or bench scraper, trim the rectangle to 9x12 inches. Cut the sheet of dough into nine 3x4 rectangles. Using a spatula, transfer the rectangles to a baking sheet that has been lined with parchment paper or a silicone baking mat. Brush the lightly beaten egg on each of the rectangles. Spoon a tablespoon of filling into the center of each rectangle, leaving a ½-inch of space around the edges.
5. Roll out and cut the second piece of dough in the exact same manner as you did the first. One at a time, place a second rectangle of dough on top of the nine assembled ones. Using your fingers, press around the seams of the dough to make sure they are sealed. Press the tines of a fork around the edges of the rectangles. Prick the tops of the rectangles in multiple spots to allow steam to escape.
6. Refrigerate the pan with the pastries (you don't need to cover them) for about 30 minutes. In the meantime, preheat the oven to 350 degrees F. Bake for 25 to 30 minutes, or until lightly browned. Cool slightly before serving. Store pastries in an airtight container at room temperature for up to one week.
* Note 1: Each filling recipes makes enough for a whole recipe (9 pop-tarts). If you make to make a few different filling, just scale back the amounts for the fillings.
* Note 2: Some additional filling ideas: Chocolate chips, Nutella, different jam flavors, dulce de leche, etc. The possibilities are endless!
* Note 3: If your kitchen runs on the warm side, you will need to refrigerate the dough for at least 30 minutes before rolling it out so that the butter doesn't start to melt.