Step 1Whisk the flour and salt in a small bowl and set aside. Place the granulated sugar in the bowl of an electric mixer or in a large bowl. Using a Microplane, finely grate the zest of the orange directly onto the sugar, scraping only the outermost layer of zest and avoiding the pith. Use your fingers to rub the zest into the sugar. Reserve the orange.
Step 2Add the butter to the sugar mixture and beat on medium-low speed or mix by hand until just combined and not at all fluffy, about 3 minutes. Add the flour mixture and beat on low speed or beat by hand until crumbly. Sprinkle the orange blossom water over the mixture and continue beating until the dough comes together in a ball. Flatten into a 1-inch-thick disk, cover tightly with plastic wrap and refrigerate until firm, at least 30 minutes.
Step 3Heat the oven to 350 degrees. Line 2 large cookie sheets with parchment paper.
Step 4On a lightly floured surface and using a lightly floured rolling pin, roll the dough to an ⅛-inch-thickness. Use a 3-inch heart-shaped cookie cutter to cut out hearts as closely together as possible. Transfer the hearts to the prepared sheets, spacing 1 ½ inches apart.
Step 5Bake one sheet at a time until golden brown, 12 to 15 minutes. Cool completely on the sheets on wire racks, then transfer the cookies to the racks.
Step 6Place the powdered sugar in a small bowl. In a separate bowl, squeeze the juice from the orange, including pulpy bits. Add 2 tablespoons juice to the powdered sugar and stir until smooth. The icing should be opaque and flow like honey. If needed, stir in more juice 1 teaspoon at a time to achieve the right consistency.
Step 7Dip the top of a cookie into the icing, coating either half the heart or the whole, then let excess drip off back into the bowl and scrape the icing off the cookie’s edge. Place on the rack, then repeat with the remaining cookies. Let stand until the icing sets, at least 1 hour.