Preheat the oven to 180C/gas 4/fan 160C. Line two baking sheets with foil to cover. In a large clean bowl, whisk the egg whites with a pinch of salt until stiff and dry. Gradually whisk in the sugar a little at a time to make a thick and glossy meringue. Tip in the pecan nuts and chocolate, then the vanilla extract and gently fold into the meringue with a large metal spoon.
Spoon heaped teaspoonfuls of the meringue mixture, spaced apart, on to the lined baking sheets. Put the sheets in the oven, then turn it off and leave the cookies for at least 3 hours, overnight or until the oven is cold.
Carefully peel the cookies from the foil. Store in an airtight tin where they will keep for 3-4 days.
Choosing vanilla extractTry Madagascar Bourbon Vanilla Extract, or an essence from Rayners, available from bumblebee.co.uk.
With walnutsYou could substitute walnuts for pecans if you prefer.