Place the butter and sugar in a small saucepan with 50 ml (2 fl oz) water. Bring to the boil, then cook on a high heat for 5 minutes until the mixture starts to turn pale. Remove from the heat and leave to cook for 2 minutes.
Stir in the cream, almonds and mixed peel.
Whisk the egg white to soft peaks, then gently fold into the almond mixture.
Spoon the mixture onto the prepared baking sheets to make 12 Florentines, leaving space between each one.
Bake in a preheated oven, 180°C (350°F), Gas Mark 4, for 15–18 minutes, until golden. Carefully slide onto a wire rack and leave to cool.
Spread the bottom of each Florentine with melted dark chocolate and leave to set.