In a large bowl, whisk together the flour, salt, and sugar. Sprinkle the cubed butter over the flour and squish it with your fingers. Work the butter into the flour until you’re left with pea-sized lumps of butter.

Add the sour cream and using a fork incorporate it into the mixture. Dump the dough onto a lightly floured surface and bring it together with a few quick kneads until you get a smooth ball, consistency of a Play-Doh (don't worry about over-working this dough). Split the dough in half, press each half into a disk and wrap tightly with plastic foil. Once the dough is wrapped into plastic, using a rolling pin, roll it over the dough to close any cracks. Refrigerate for at least 2 hours.

Preheat the oven to 200 °C (400 °F). Line two baking sheets with parchment paper.

Lightly flour the work surface and the rolling pin, and roll out the dough to about 3-4 mm (1/8-inch) thick. Using a 9 cm (3.5-inch) round cookie cutter, cut out as many circles from the dough as you can. Re-roll any scraps of dough and cut more circles. I got 14 circles from every piece of the dough.

Divide half of the filling among seven circles. Brush a little bit of water along the edges of each filled or circle and then place the other half of the pastry circles on top. Press all around the edge with your fingertips to seal then use a fork to crimp. Using a small knife, cut a vent on top of each hand pie. Brush the top of each pie with the beaten egg, and sprinkle with sugar. Transfer the pies to a prepared baking sheet.

Bake the pies for 20-25 minutes until golden brown, rotating pans halfway through. Remove them from the oven, and let cool for 20 minutes before serving.

Repeat the process with the other half of the dough and the filling.