Line two baking sheets with parchment paper and have a pastry bag with a plain tip (about 1/2-inch, 1 cm) ready.

Grind together the powdered sugar with the almond powder and ground poppy seeds so there are no lumps; use a blender or food processor. 

Using a mixer beat the egg whites until they begin to rise and hold their shape. While whipping, beat in the granulated sugar until very stiff and firm, about 2 minutes.

Fold the dry ingredients, in two batches, into the beaten egg whites with a rubber spatula. When the mixture is smooth and there are no streaks of egg white, stop folding and scrape the batter into the pastry bag. (standing the bag in a tall glass helps if you’re alone).

Pipe the batter on the parchment-lined baking sheets in 1inch (2 cm) circles, evenly spaced one-inch (2 cm) apart.

Rap the baking sheet a few times firmly on the counter top to flatten the macarons and sprinkle poppy seeds in top of each. Let them rest at room temperature. A skin needs to form, and it can take 30-90 minutes,depending on the weather. If you touch them lightly and the top has dried, and nothing sticks to your finger, they’re ready to bake. Bake them for 15-18 minutes. Let cool completely then remove from baking sheet.

Spread a bit of batter on the inside of the macarons then sandwich them together. 

Let them stand at least one day before serving, to meld the flavors.