I searched for recipes in books and online and the King's Arthur Flour recipe was the best i found and the one i followed. And i'm gonna be really lazy and copy and cut the recipe... and added a few remarks by me in dark print.
2 cups (8 ½ ounces) King Arthur Unbleached All-Purpose Flour
1 tablespoon sugar
1 teaspoon salt
1 cup (2 quarter-pound sticks, 8 ounces) unsalted butter, cut into pats
1 large egg
2 tablespoons (1 ounce) milk
12 teaspoons Nutella
1 egg, beaten well to brush the pastry before filling
Make the dough: Whisk together the flour, sugar, and salt. Work in the butter until the mixture holds together when you squeeze it, with pecan-sized lumps of butter still visible. Mix the egg and milk, and add it to the dough, mixing just until everything is cohesive. ( Rich and Sweet: I used the food processor on mine even though this recipe doesn't call for one, just lightly pulse a few times to cut butter into flour and then i poured the dough on my countertop and added the milk and egg and kneaded lightly by hand. DO NOT OVERMIX or you will have hard pop tarts)
Divide the dough in half; each half will weigh about 10 ounces (about 280g). Shape each half into a rough 3" x 5" rectangle, smoothing the edges. Roll out immediately; or wrap in plastic, and refrigerate for up to 2 days.
Assemble the tarts: If the dough has been chilled, remove it from the refrigerator and allow it to soften and become workable, about 15 to 30 minutes. Place one piece on a lightly floured work surface, and roll it into a rectangle about 1/8" thick, large enough that you can trim it to an even 9" x 12". Laying a 9" x 13" pan atop the dough will give you an idea if you’ve rolled it large enough. Trim off the edges; place the scraps on a baking sheet, and set them aside, along with the 9" x 12" rectangle of dough.
(RICH AND SWEET: I divided the dough into 12 equal pieces and wrapped them individually as it was easier for me to roll them out one at a time into a 3"x4" rectangle)
Roll the second piece of dough just as you did the first. Press the edge of a ruler into the dough you’ve just rolled, to gently score it in thirds lengthwise and widthwise; you’ll see nine 3" x 4" rectangles.
Beat the egg, and brush it over the entire surface of the dough. Place a heaping tablespoon(RICH AND SWEET: I used 1 teaspoon and thought it was plenty) of filling into the center of each marked rectangle. Place the second sheet of dough atop the first, using your fingertips to press firmly around each pocket of jam, sealing the dough well on all sides. Press the tines of a fork all around the edge of the rectangle. Cut the dough evenly in between the filling mounds to make nine tarts. Press the cut edges with your fingers to seal, then press with a fork, to seal again.
Gently place the tarts on a lightly greased or parchment-lined baking sheet. Prick the top of each tart multiple times with a fork; you want to make sure steam can escape, or the tarts will become billowy pillows rather than flat toaster pastries. Refrigerate the tarts (they don’t need to be covered) for 30 minutes, while you preheat your oven to 350°F.
Sprinkle the dough trimmings with cinnamon-sugar; these have nothing to do with your toaster pastries, but it’s a shame to discard them, and they make a wonderful snack. While the tarts are chilling, bake these trimmings for 13 to 15 minutes, till they’re golden brown.
Remove the tarts form the fridge, and bake them for 25 to 35 minutes(RICH AND SWEET: 20 minutes was plenty of time for mine), until they’re a light golden brown. Remove them from the oven, and allow them to cool on the pan. ( RICH AND SWEET: i removed them from pan with a spatula and cooled them on a rack)