Heat oven to 180C/fan 160C/gas 4. Line a 1kg loaf tin with baking parchment, making sure the paper comes up higher than the sides. Beat the butter and sugar together until fluffy, then add the eggs, a little at a time, along with the vanilla. Fold in the flour until you have a smooth mixture.
Dust the cherries in a little flour, then carefully stir half of the fruit and chocolate into the mixture. Spoon into the prepared tin, then scatter the remaining cherries and chocolate on top, pressing them in lightly. Bake for 1 hr 10 mins - 1 hr 15 mins until a skewer inserted into the middle comes out clean. Make sure you don't mistake melted chocolate for raw cake mix. Leave to cool in the tin for a few mins, then turn out on to a wire rack and leave to cool completely. This can now be wrapped tightly in cling film and stored in the fridge for up to 3 days.
Remove the marscapone from the fridge to come to room temperature. Melt the white chocolate in a bowl over a pan of hot water. Quickly stir in 1 tbsp of the marscapone, then beat in the rest (be careful not to overbeat the mixture or it will go grainy). Spread over the top of the loaf and finish with white chocolate curls or fresh cherries.