Combine flour, 1 tablespoon sugar, and salt in a bowl. Add the ice-cold cubed butter and mix with your fingertips or a pastry cutter for about 5 minutes until the mixture resembles coarse breadcrumbs with some pea-sized pieces of butter remaining. This texture is crucial for creating flaky layers in your hand pies. Add the ice-cold water and vanilla extract, then gently mix just until the dough comes together—don't overwork it or the pies will be tough. Form the dough into a disk, wrap it in plastic wrap, and refrigerate for at least 2 hours (or up to overnight). I find that chilling the dough longer actually improves the flavor and makes it easier to work with.
Combine the fresh raspberries, 1/2 cup sugar, lemon juice, and 1/4 cup water in a saucepan over medium heat. Simmer for about 5 minutes, stirring occasionally, until the raspberries break down and release their juice. Pour the mixture through a fine-mesh strainer into a bowl, pressing gently on the solids to extract all the liquid while leaving most of the seeds behind. Return the strained liquid to the pan and whisk the cornstarch with 1 tablespoon of water to create a slurry, then stir it into the raspberry juice. Simmer over medium heat for 2-3 minutes, stirring constantly, until the filling thickens and turns glossy and translucent. Transfer to a bowl and refrigerate until completely cold—this step is essential so the filling doesn't melt through the pastry during baking.
In a small bowl, whisk together the beaten egg with 1 teaspoon water to create an egg wash—this will give your hand pies a beautiful golden sheen. In another small bowl, combine the icing sugar and Biscoff cookie crumbs. Set both bowls aside so they're ready when you need them.
Remove the chilled dough from the refrigerator and let it sit for 5 minutes to soften slightly for easier rolling. On a lightly floured surface, roll the dough to about 1/8-inch thickness. Using a 3-inch round cutter (or a glass), cut out circles—you should get about 12-14 circles depending on your cutter size. Place 1 teaspoon of the chilled raspberry filling from Step 2 on one half of each circle, leaving a 1/2-inch border. Brush the edges with the egg wash from Step 3, then fold the circle in half and press the edges firmly together. Using the tines of a fork, press around the sealed edges to create a decorative pattern and ensure a tight seal. Arrange the sealed pies on a parchment-lined baking sheet, brush the tops with more egg wash, and sprinkle with a tiny pinch of the Biscoff-sugar mixture if desired.
Preheat your oven to 360°F. Bake the hand pies for 18-20 minutes until the pastry is light golden brown—watch them carefully as oven temperatures can vary. Remove from the oven and let cool on the baking sheet for 5 minutes, then transfer to a wire rack to cool completely. I like to dust them with the icing sugar and Biscoff crumb mixture while they're still warm so it adheres nicely, which adds a delightful texture and flavor contrast to each bite.
