Whiz the flour, cocoa powder and icing sugar together in a food processor for a few seconds. Add the butter and blend to form crumbs, then pour in the egg and 1 tablespoon water, and pulse until the mixture begins to come together (add more water if necessary). Knead the pastry until smooth on a lightly floured surface. Wrap in clingfilm and chill for 1 hour.
Roll out the pastry on a lightly floured surface. Using a 12 cm (5 inch) tartlet tin or saucer as a guide, cut out circles. Knead the trimmings together gently, re-roll the pastry and cut out some more circles.
Grease a 12-hole deep muffin tin (not a regular patty tin) or line with paper muffin cases. Ease the pastry circles into the tins and chill for 15 minutes. Spoon in the mincemeat and sprinkle over the pecan and chocolate pieces.
Press the pastry edges up and over the filling to make a rim. Brush the tops with apricot glaze or cranberry jelly and bake in a preheated oven, 200°C (400°F), Gas Mark 6, for 30 minutes. Cool in the tin. Remove from the tin and cases and dust with icing sugar to serve.