Preheat your oven to 280°F (140°C) and line a cookie sheet with a silicone mat or parchment paper.

Pulse together powdered sugar and almond flour in a food processor until fine, then sift into a bowl. Fold in poppy seeds.

Whip egg whites in a clean bowl until frothy, gradually adding granulated sugar until stiff peaks form.

Fold one-third of the meringue into the dry ingredients, then add remaining meringue in two additions until batter flows smoothly.

Pipe 1-inch disks onto the prepared baking sheet and tap to release air bubbles.

Allow shells to rest at room temperature for about 1 hour until tops feel dry.

Bake macarons for 15 minutes, rotating halfway, until they lift cleanly from the mat.

Let the macarons cool on the baking sheet for 10 minutes before transferring to a wire rack.

Combine granulated sugar, lemon juice, whole egg, and egg yolk over simmering water, whisking until thickened, remove and add butter.

Whip heavy cream until stiff peaks form and fold into cooled lemon curd.

Pipe whipped lemon curd onto half of the macaron shells and top with remaining shells to assemble.