In a large bowl, beat the butter and sugar with an electric hand mixer until smooth and creamy. Add the vanilla and beat until well mixed.
Stir in the flour and salt until well mixed. Form the dough into a square, wrap in saran wrap and chill 20-30 minutes.
Once chilled, roll the shortbread between two layers of parchment paper (one on the bottom, one on top of the shortbread dough) until about 1/2 inch thick - you should have roughly a 10x8 inch square.
Cut into 24 squares that are 2x1.5 inches big and then gently transfer the parchment paper onto a cookie sheet.
Whisk the egg white and water until well mixed and brush on top of each cookie. Sprinkle with granulated sugar.
Bake until the edges are JUST golden brown, about 12-14 minutes (they set up a lot!) Cool on the pan COMPLETELY
DEVOUR
Notes
*Please weigh your flour to ensure accurate results