In a large bowl, stir together the flour and salt. Add in the cubed butter. Use your fingers to pinch and break up the butter into small pieces while mixing the pieces into the flour.
Make a well in the middle of the flour and pour in the cold water. Use your hands to mix the flour into the water until it becomes a shaggy dough. Turn the dough out onto the counter.
Use your hands to press the dough and crumbs together. Flatten it slightly and fold it over onto itself about 5 times to create rough layers of flattened butter between the flour. Shape the dough into a disc, wrap with plastic wrap, and chill in the fridge for at least 2 hours or overnight.
In the meantime, stir together the strawberries, sugar, water, and vanilla extract in a small pan on medium heat. Let the mixture boil for about 10 minutes or until it has thickened. Transfer the strawberry compote to a bowl to cool.
When you're ready to assemble your hand pies, preheat the oven to 375F and line a baking sheet with parchment paper. Roll out your dough to about ⅛" thick. Use a knife or square cookie cutter to cut the dough into 5x5" squares.
Spoon 1-2 tablespoons of strawberry compote in one corner of each square. Fold the other corner over to make a triangle and use a fork to press and seal down the edges.
Brush hand pies with egg wash and sprinkle with sugar crystals (optional). Bake pies for about 30 minutes or until golden brown.
Stir the powdered sugar and milk together and spoon over each hand pie. Enjoy while warm.