Rub the butter into the flour, then stir in the yeast, sugar and salt. Beat the whole eggs and yolks together and stir into the dry ingredients with the mixed fruit and peel.
Knead the very soft dough on a lightly oiled surface with two plastic scrapers for 10 minutes or until smooth and elastic. This stage can also be done in a free-standing mixer fitted with a dough hook.
Leave the dough to rest in a lightly oiled bowl, covered with oiled clingfilm, for 2 hours or until doubled in size.
Knead the mixture again briefly, then shape it into a round ball with your hands. Transfer the dough to a deep 20 cm | 8-inch round cake tin lined with a panettone case. Cover with oiled clingfilm and leave to prove for 2 hours or until doubled in size.
Meanwhile, preheat the oven to 180°C (160° fan) | 350F | gas 4.
Remove the clingfilm and bake the panettone for 40 minutes or until golden brown and cooked through. Leave to cool completely on a wire rack before dusting with icing sugar.