Freeze butter. Grate it and freeze it again.
Whisk flour, sugar, and salt together. Add frozen butter. Add ½ cup of cold water and mix with a spatula. If the dough hasn´t come together yet, add more water, but only a tablespoon at a time (mine needed 2 more tablespoons).
Knead it gently, only until the dough comes together. You want to see little pieces of butter like the picture above. Divide the dough into 3 equal portions. Chill the dough for about an hour or freeze it for 20 minutes before rolling.
I prefer to roll my dough on parchment paper. It makes it easier to transfer the dough and it doesn´t need as much flour as when done on the counter.
Flour the parchment paper, put the dough in the center, add a little more flour and cover it with another piece of paper. Roll out the dough. If your dough is still firm, you can cut in now. If you see that starts to soften, slide it onto the back of a tray and chill it in the freezer until firm again.
Cut the dough with a cookie cutter. Put the hearts on a tray lined with parchment paper. Brush the borders around the filling with egg wash. Place a second dough heart on top of each filled heart. Brush each pie with egg wash.
Bake at 425°F / 218°C for about 15 minutes or until golden brown. Remove the pies from the oven and allow them to rest for 10 minutes before drizzling some icing.