Preheat the oven to 180C/350F/Gas 4. Line three baking trays with baking parchment or silicon sheets.
Measure the butter, sugar and syrup into a small pan and heat gently until the butter is melted. Remove from the heat and add the flour, chopped cranberries or cherries, candied peel and nuts to the pan. Stir well to mix.
Make 18 florentines by spooning six teaspoonfuls of the mixture on to each of the prepared baking trays, leaving plenty of room for them to spread during cooking.
Bake for 8-10 minutes, or until golden-brown. Leave the florentines to cool before lifting onto a cooling rack using a palette knife (if the florentines have been baked on greased baking trays, then allow them to harden for a few moments only before lifting onto cooling racks to cool completely). If the florentines become too hard to remove, then pop them back into the oven for a few minutes to allow them to soften.
Set a heatproof bowl over a pan of simmering water, without letting the bowl touch the water. Temper the chocolate by breaking half of the chocolate into the bowl. Stir until the chocolate reaches a melting temperature of 53C/127F. Meanwhile, finely chop or grate the remaining chocolate.
Carefully remove the bowl from the pan, add the rest of the chocolate and stir gently until the chocolate has cooled to 26C/79F.
Spread a little melted chocolate over the flat base of each florentine and leave to cool slightly before marking a zigzag in the chocolate with a fork. Leave to set, chocolate side up on a cooling rack. Store in an airtight container.