Rose Pistachio Shortbread Cookies

In a heavy-duty mixer fitted with the paddle attachment, beat 1 cup cubed cold butter (2 sticks) for 1 minute on medium speed. Add the ⅔ cup granulated sugar and ½ teaspoon rose water. Continue beating on medium-high speed until the mixture is smooth and satiny, like thick mayonnaise (this can take 5 minutes or more depending on the temperature of your kitchen).

Scrape down the bowl with a spatula, then add the flour mixture on low speed until it's incorporated. Stir ⅓ cup shelled pistachios and 1 tablespoon of the rose petals (if using). The dough will be crumbly and not quite hold together - that's okay.

Transfer the dough to a work surface and gently squeeze and push the dough together to form a ball. Divide the dough in half and roll into firm logs about 6 inches long. Wrap in plastic and refrigerate until firm, 2 hours or more. 

Preheat oven to 350 (175 C) degrees with the racks arranged in thirds. Line two rimmed baking sheets with parchment paper.

Brush the logs with 1 lightly beaten egg white. Combine the remaining 2 tablespoons pistachios and 1 tablespoon rose petals on a large plate or shallow pan. Roll the logs in the mixture to coat.

With a thin, sharp knife, slice the logs into ½-inch-thick cookies (not any thinner or the cookies won't hold their shape) and arrange on the baking sheets.

Bake 12-15 minutes, rotating the sheets from top to bottom and front to back halfway through, until the edges begin to turn light golden. The cookies will be soft, but will firm as they cool.

Transfer to a rack to cool completely.