Pulse the almond flour and powdered sugar in a food processor until fine, then sift into a bowl, discarding any large bits. Stir in half the egg whites to make a thick paste.

Heat the remaining egg whites with the granulated sugar and salt over a simmering water bath, whisking, until the sugar dissolves and the mixture reaches about 160°F (71°C) — or until it feels smooth between your fingers with no grit. Whip on high speed to glossy, stiff peaks that hold their shape when the whisk is lifted.

Fold the meringue into the almond paste in thirds (macaronage) until the batter flows like thick lava and falls in a ribbon that disappears back into the bowl in about 10 seconds. If using color, add it with the last third.

Pipe 1 1/4-inch (3 cm) rounds onto parchment-lined sheets, 1 inch apart. Rap each sheet firmly on the counter to release air bubbles, then pop any surface bubbles with a toothpick.

Rest the piped shells for 30–60 minutes, until a dry skin forms — a fingertip touched lightly to a shell comes away clean. On humid days this can take longer; do not rush it.

Bake at 300°F (150°C) for 14–16 minutes. The shells should not wobble on their feet. Cool completely on the sheet before peeling them off.

Fill the shells with ganache, buttercream, or jam, sandwiching them in pairs of similar size.

For the best texture, mature the filled macarons in the fridge overnight before serving — the filling softens the chewy interior. Serve cold or at room temperature.