Preheat the oven to 170˚C (fan oven 150˚C, 325˚F, gas 3). Grease and line 2 x deep 18cm (7 inch) round cake tins. Whisk the butter and sugar together in a large bowl for 2-3 minutes until creamy and well blended. Gradually whisk in the milk, with a little of the flour, then sift the remaining flour and Baking Powder on top and gently mix until well combined.
In a large, grease-free bowl, make up the Egg White Powder as directed until softly foaming, then gently fold into the cake mixture.
Divide the mixture equally between the prepared tins, smooth the tops and bake for about 50 minutes until risen, lightly golden and firm to the touch. Cool for 5 minutes then turn on to wire racks to cool.
Slice a thin layer from the tops of both cakes. Crumble the cake trimmings and put to one side for making the snowball truffles – you will need 100g (3 ½ oz) cake crumbs. Carefully slice through the middle of each cake to make 4 equal rounds.
To decorate, line a large baking tray or heatproof board with baking parchment. Put the granulated sugar in a small saucepan with 150ml (1/4 pt) water. Heat gently, stirring, until the sugar dissolves, then bring to the boil, stop stirring, and boil steadily for 15-20 minutes until thick and syrupy, but clear and uncoloured – 140-145°C (284-293F°) on a sugar thermometer. Try to avoid boiling the mixture too rapidly as it will spit sugar crystals up the side of the saucepan and these will caramelise and discolour the syrup. Remove from the heat, quickly whisk in 1.25ml (1/4 tsp) Peppermint Extract, and immediately pour over the centre of prepared baking tray or board (take car, melted sugar will be very hot). Spread out in an even layer to form a rectangle approx. 20 x 30cm (8 x 12inch). Leave to set slightly for a couple of minutes, then as the sugar begins to firm up, score the surface into long shard shapes using a large bladed knife – this will help you snap the sugar cleanly once it is fully set. Leave in a cool, dry place (not the fridge) for a further 30 minutes or until completely set.
Next make the snowball truffles. Chop up 50g (2oz) Regal Ice and put in a small saucepan. Add 5ml (1tsp) water and heat very gently, stirring occasionally until melted together. Remove from the heat. Stir the reserved cake trimmings and 1.25ml (1/4 tsp) Peppermint Extract. Mix well and leave aside for about 30 minutes to firm up. Form into different sized balls. You should be able to make at least 12 cake balls of varying sizes.
Sift 50g (2oz) icing sugar in a bowl and carefully coat the balls all over to give them a snowy finish. Put on a board lined with baking parchment and leave in a cool, dry place to firm up. Avoid refrigerating for any length of time as this will make the icing sugar dissolve. Keep the bowl of icing sugar for later use.
For the filling and covering, put the butter in a bowl and beat until smooth and glossy. Gradually sieve and mix in the remaining 250g (9oz) icing sugar and sufficient milk to make a smooth, spreadable icing. Stir in 2.5ml (1/2 tsp) Peppermint Extract. Spread 225g (8oz) of the Peppermint icing evenly over 3 sponges and stack them all on top of each other.
Measure round the outside of the cake for the circumference and then measure the depth of the cake. Use 100g (3 ½ oz) the remaining Peppermint icing to spread thinly round the sides of the cake – this will help the Regal Ice stick to the cake.
Gently knead 600g (1lb 5oz) Regal Ice until pliable. Lightly dust the work surface with icing sugar and roll out the Regal Ice to the thickness of a £1 coin. Using assorted sized snowflake cutters, stamp out about 30 different shapes and place on a tray lined with baking parchment. Cover loosely with more parchment and put the tray in a dry, cool place for at least 2 hours until the shapes are dry and firm enough to be able to arrange on top of the cake and around the serving plate. Ideally leave overnight to dry out further.
Lightly dust the work surface with icing sugar and roll out the remaining Regal Ice to form a circle approx. 32.5cm (13 inch) diameter. Using your rolling pin to help you lift the icing circle, drape it over the cake. Smooth into position using the palm of your hand, working from the centre to the edge and down the sides. Trim away the excess icing. To achieve an extra smooth finish, dust your hand with a little icing sugar and gently rub the cake all over to buff the surface. Leave in a cool place to allow the surface to dry for at least 2 hours (preferably overnight).
To finish the decoration, chop the remaining Regal Ice and place in a saucepan and add 30ml (2 tbsp) water. Heat very gently, stirring occasionally, until melted together. Remove from the heat, mix in the remaining Peppermint Extract and beat until smooth. Working quickly, spoon the molten Regal Ice round the top edge of the cake so that it dribbles down the sides in thick drips. As it cools, this icing thickens quickly, but can be gently reheated to soften again, if necessary.
Spoon the remaining melted Regal Ice in the centre of the cake and smooth over the top so that it meets the dripping edge. Leave to cool and set for about 1 hour.
When you are ready to serve the cake, lay a large sheet of baking parchment on the work surface and place the cake in the centre. Cover up the edges of the serving plate or board with parchment or, you may find carefully laid cling film easier to use as a covering. Spray or brush over the cake with silver lustre to give it a frosted look. Leave to dry for 5 minutes then remove the plate protection.
Lightly dust the snowball truffles with the reserved icing sugar and arrange on and around the cake. Break up the peppermint into shards and press into the centre of the cake to resemble ice. Decorate the top and around the cake with snowflakes, and add candy canes if using. Your stunning snow and ice cake is now ready to serve and impress!