Preheat oven to 350 degrees Fahrenheit.
In a large bowl, combine 2 ¼ cups flour, baking powder, and 1 teaspoon salt.
Using a pastry blender or 2 knives, cut butter into flour mixture until mixture resembles coarse sand.
Add 1 egg yolk, ½ c chilled water, and ½ teaspoon vanilla, and mix until just combined. If dough is dry or crumbly, add up to 3 tablespoons more chilled water).
Transfer dough to a lightly floured surface and knead 2 to 3 times, just until dough comes together. Return dough to bowl, cover with plastic wrap, and refrigerate until chilled, about 15 minutes.
Meanwhile, make filling: In a medium bowl, combine strawberries, confectioner’s sugar, and jam, plus remaining flour, vanilla, and salt. Set aside.
In a small bowl, beat remaining yolk and 1 tablespoon water for egg wash. Set aside.
On a lightly floured surface, roll out dough to ½ inch thickness. Using a 3 inch round cookie cutter, cut dough into 6 rounds. Roll 1 round into a 6 inch circle.
Spoon a heaping 2 tablespoons filling onto half of circle, leaving ½ inch border. Brush the edges with egg wash, then fold dough over filling. Using a fork, crimp the edges to seal. Transfer to a parchment lined baking pan. Repeat with remaining dough rounds and filling.
Using a toothpick, poke a few holes in the top of each pie. Brush with remaining egg wash and sprinkle each pie with ½ teaspoon sanding sugar.
Bake until golden brown, or 30 to 35 minutes. Transfer to wire rack to cool.