In a saucepan, gently heat 300ml of double cream over medium heat until it just begins to boil. Remove from heat and stir in 200g of milk chocolate, 200g of dark chocolate, 50g of unsalted butter, and 1/2 tsp of sea salt until melted and smooth.

Transfer the ganache to a bowl and cover with plastic wrap, ensuring it touches the surface. Refrigerate for about 3 to 4 hours, or overnight, until firm.

Once firm, scoop out small amounts of ganache and roll between hands to form truffles. Arrange on a plate and refrigerate for 15-20 minutes.

Melt an additional 200g of milk chocolate in a microwave-safe bowl in 30-second intervals until smooth.

Dip each truffle into the warm melted chocolate using a fork, allowing excess to drip off, and place on a greaseproof paper-lined tray.

Let the truffles set in the fridge for about 1 hour.

Prepare decorations by rolling out green fondant for holly leaves and shaping red fondant for berries. Decorate the truffles with royal icing, fondant leaves, and berries.

Allow decorated truffles to set briefly before arranging in gift boxes or on a plate to serve.