Breads: Pistachio Croissants

1/4 cup water
1/2 cup sugar, divided
3/4 cup shelled, unsalted pistachios
1/2 t kosher salt
3 T unsalted butter at room temp
1 large egg, lightly beaten
1 t vanilla
4 day-old croissants, split in half lengthwise
Confectioners' sugar

Preheat oven to 350 F.  In small saucepan set over med-hi heat, add water and 1/3 cup sugar.  Cook until sugar dissolves, about 2 mins.  Turn off heat and set aside.  In food processor, combine 1/2 cup plus 2 T pistachios, salt, and remaining sugar;  pulse until nuts are finely ground.  Add butter and process until combined.  Add egg and vanilla and pulse just until combined, stopping the food processor to scrape down sides and bottom as necessary.  Brush cut side of each croissant half with some of the simple syrup mixture, then spread 2 T of nut mixture on bottom half and cover with a top half, pressing down to slightly flatten the croissants.  Arrange on parchment paper lined rimmed baking sheet.  On a cutting board, finely chop remaining 2 T nuts.  Brush croissants with more simple syrup and sprinkle the chopped nuts on top.  Bake until golden and filling fuses the top and bottom halves together, abt. 25 mins.  Remove from oven and cool 20 mins before sprinkling with confect. sugar.  Serve.