Line 2 baking sheets with parchment paper or silicone macaron mats. Fit a large piping bag with a round tip (about 1/2 inch), or be ready to snip the end of the bag later.

In a medium bowl, whisk together the almond flour and 200 g powdered sugar. Sift the mixture through a fine-mesh sieve into another bowl, pressing gently with a spoon and discarding any large bits to ensure smooth shells.

In a clean, grease-free bowl, add the egg whites, fine sea salt, and cream of tartar. Using a stand mixer with the whisk attachment or a hand mixer, beat on medium speed until the egg whites look foamy, about 1–2 minutes.

With the mixer running, gradually add the granulated sugar, about 1 tablespoon at a time. Continue beating on medium-high until you reach stiff, glossy peaks, 5–7 minutes more. The meringue should hold a straight peak when you lift the whisk.

Beat in 1 teaspoon vanilla extract for a few seconds. If using, add a small amount of gel food coloring and mix just until evenly tinted; remember the color will fade slightly when baked.

Add about one-third of the almond flour mixture to the meringue and gently fold with a rubber spatula, going around the bowl and then through the center. Repeat in two more additions until all the dry ingredients are incorporated. The batter will be stiff at first; continue folding gently.

Continue folding until the batter flows slowly off the spatula like thick lava, forming ribbons that disappear back into the bowl in about 10–15 seconds. If it breaks in chunks, fold a few more times; if it runs like pancake batter, it is overmixed.

Transfer the batter to the piping bag. Pipe 1 1/4-inch rounds onto the prepared trays, spacing them about 1 inch apart. Hold the bag straight up, squeeze to form a round, then stop and twist your wrist slightly to finish each circle.

Firmly tap each baking sheet on the counter 4–5 times to release air bubbles. Pop any visible large bubbles on the surface with a toothpick for smoother tops.

Let the piped macaron shells sit at room temperature for 25–45 minutes, depending on humidity, until the tops look dull and you can gently touch one without batter sticking to your finger. This helps create the classic ruffled feet.

Preheat the oven to 300°F (150°C). Bake one tray at a time on the middle rack for 15–18 minutes. The shells are done when they no longer wiggle much if gently nudged and the tops feel set, not jiggly.

Remove the trays from the oven and let the shells cool on the baking sheets for at least 15–20 minutes. Carefully peel them off the parchment or mats. If they stick badly, they likely need another minute or two of baking next time.

Beat the softened butter on medium speed until creamy, about 2 minutes. Add 240 g powdered sugar, 1 teaspoon vanilla extract, a pinch of fine sea salt, and 1 tablespoon cream or milk. Beat on low to combine, then increase to medium and mix until fluffy and smooth. Add more cream or milk, a little at a time, to reach a spreadable consistency.

Match the cooled shells in pairs of similar size. Pipe or spread a small dollop of vanilla buttercream onto the flat side of one shell, then top with its partner and gently twist to spread the filling to the edges without overfilling.

Place the filled macarons in an airtight container and refrigerate for 12–24 hours before serving. This resting time softens the shells slightly and allows the flavors to meld for a true bakery-style texture.