In medium bowl, sift together almond flour and powdered sugar twice. Set aside.

In a large mixing bowl with whisk attachment, beat the egg whites on medium speed until foamy. Add cream of tartar and continue to beat. Slowly add sugar one tablespoon at a time. Increase the speed to medium-high/high and beat until hard peaks. Add lemon zest, vanilla extract, lemon juice and yellow food coloring. Beat on medium-high speed for one more minute.

Sift the almond flour/powdered sugar mixture over the whipped egg whites. Gently fold the mixture together.

Transfer the batter into a pastry bag with a large round tip.

Pipe out 1.5-inch rounds about an inch apart on two baking sheets lined with silpat or parchment paper (do not use an unprotected baking sheet).

Tap the baking sheets firmly on the counter a few times to get rid of any air bubbles.

Let the macarons rest and dry for 15-30 minutes. On a humid day, it might take an hour or so. To see if it’s ready to be baked, lightly touch it. If the batter doesn’t stick to your finger, then it’s ready.

Preheat the oven to 300°F (150°C).

Bake the macarons for 9 minutes. Then open the oven to let out moisture. Close door and cook 4-6 more minutes.

Transfer to wire rack to cool for 15 minutes, and then remove from the baking sheets.

While macarons are drying, prepare the lemon buttercream. In a mixing bowl with whisk attachment, beat the butter until fluffy. Add powdered sugar, heavy cream, lemon juice, lemon zest and and beat until well combined.

Transfer the buttercream into a pastry bag and fill the macarons. It’s best to serve macarons the next day. The baked part absorbs flavor from the filling over time.