Preheat the oven to 300F and line 2 baking trays with parchment paper.
Whip the whites and meringue powder until they are foamy, then slowly add the sugar and whip just until the whites barely hold a soft peak when the beaters are lifted. It is very important not to overwhip your egg whites). Stir the ground almonds and icing sugar together and then fold this into the whipped whites in 2 additions (the batter will be quite runny).
If you wish to colour the macarons, divide the batter into 3 bowls and stir in a touch of colour into each. Fill 3 piping bags fitted with a plain tip with each of the batters and pipe macarons that are 1 1/2 -inches wide and an inch apart on the baking tray. Let the macarons sit for 10-30 minutes, until they develop a “skin” (until the surface of the macarons appear dull – no longer shiny). Bake for about 10 minutes, until they lift off the parchment paper using a spatula without sticking. Let them cool on the trays before removing.
To assemble, pipe or spread a little curd or marmalade on the bottom of one macaron and press the bottom of a second onto it, pressing gently. Continue until all of the macarons are filled.
The macarons will keep for up to 3 days in airtight container.
**Extra fine ground almonds can be found at fine food stores, but if you cannot buy them, then sift conventional ground almonds to achieve a finer texture and then measure, or another option is to grind them with the icing sugar to have them to achieve that fine texture.