Preheat oven to 350 degrees. Line a baking sheet with parchment paper.
Prepare the chocolate version of the perfect pie crust recipe. Following the rolling method in the gluten free pie crust recipe, roll the dough into an oval about 13” by 9” and about ¼” thick. Transfer the rolled dough to the prepared baking sheet. Brush any excess flour off the dough. Roll and fold the edge of the dough over to form a rimmed crust. Bake for 15 minutes or until the dough is fairly firm. Leave oven on.
Melt the chocolate in the microwave for about 2 minutes or until most of the chocolate is melted. Alternately place the chocolate chips in a heat proof bowl and place on a pan with an inch or two of barely simmering water until melted. Stir in the espresso powder and continue stirring until all the chocolate is melted. Let cool slightly.
Beat the egg whites and salt in the bowl of an electric mixer fitted with a whisk attachment until foamy, starting on low speed and increasing to high. Gradually add the sugar and beat until stiff peaks form. Add the vanilla extract and mix well. Fold the chocolate into the egg whites until the mixture is no longer streaky. Spread the filling over the baked crust evenly, it should be about ½ inch thick. Sprinkle the chopped pistachios over the top. Return to the oven and bake for another 10 minutes or until the filling looks a bit dry and has cracked slightly. Let cool on the pan for 5 minutes and then transfer to a wire rack to finish cooling.
Once the galette has cooled, drag a vegetable peeler across the side of the white chocolate square and let the curls of chocolate fall over the top of the galette. Serve slightly warm or cool. Can be made a day ahead, cover with plastic wrap and store in the fridge.