Sift powdered sugar, almond flour, and ground pistachios together twice, discarding any large pieces that won't pass through the sieve.

Beat egg whites on medium speed until foamy, then add granulated sugar gradually and beat on high until the meringue holds a stiff, glossy peak, about 5 minutes. Add food coloring if using.

Fold the dry ingredients into the meringue in three additions, deflating the batter deliberately until it flows off the spatula in a slow ribbon and a dropped dollop settles flat within 20 seconds.

Pipe 1 1/2-inch rounds onto parchment-lined baking sheets, spacing 1 inch apart.

Tap each sheet firmly on the counter 3 or 4 times to release air bubbles, then let the shells rest uncovered for 30 to 45 minutes, until a finger touched to the surface comes away clean with no batter sticking.

Preheat oven to 300F while the shells rest.

Bake one sheet at a time for 14 to 16 minutes, until the shells have risen with a visible "foot" and do not wobble when nudged. Cool completely on the pan before removing.

Beat butter until smooth, then add powdered sugar, ground pistachios, and rosewater, beating until light and fluffy, about 2 minutes.

Match the macaron shells by size, then pipe filling onto half of them and sandwich with the remaining shells.

Finish a few macarons with a crumble of dried rose petals and small flecks of gold leaf, then refrigerate in an airtight container for at least 24 hours before serving for the best texture.