Combine the flour, sugar, and salt in a large bowl.
Add the butter and work with your fingers until it looks like coarse crumbs.
Add 3 tbsp. of cold water into the mixture and continue mixing it in. Work the dough into a ball (you may need to add another tablespoon of cold water to get the desired consistency).
Flatten the dough ball into a disk and wrap it up tightly in a large piece of parchment paper (the parchment paper should be the length of your baking pan). Refrigerate for 30 minutes.
Preheat oven to 400°F. Take the dough out of the fridge and let sit for about 5 minutes before rolling out, to help prevent cracks.
In a medium bowl, combine the raspberries with the sugar, cornstarch and salt.
Roll the dough out on a lightly floured surface or directly on the parchment into a large circle, about 12”-14” in diameter (⅛" thickness is ideal). It doesn’t have to look perfect! The more rustic, the better. Carefully transfer the parchment with the dough onto a rimmed baking sheet or pizza pan.
Spoon the fruit filling into the center of the circle, leaving a 2” to 3” border of dough around the filling.
Fold the dough border over the fruit, overlapping a little as you go (remember not to worry about perfection here). The center will remain open.
Bake for 35-45 minutes in the preheated oven, until the pastry is golden and fruit is bubbling.
Transfer to a wire rack and let cool before serving.
Make sure to use a rimmed baking pan to catch any drippings that might occur during baking.
To get a cleaner cut circle, simply trim around the edges of the dough after rolling it out.
Make sure the butter and water are cold when making the pastry dough. This will help the dough keep its shape.