1. Grease and line 3 x 20cm round baking tins with baking parchment, and preheat the oven to 170ºC, gas mark 3.
2. Place the butter, sugar, flour, baking powder and salt into the bowl of a stand mixer with paddle attachment. Mix on low until all the butter is rubbed into the dry mixture and it has a sandy texture.
3. In a small jug, beat together the milk, eggs and vanilla. Keeping the mixer on a low speed, pour the mixture down the side of the flour and butter bowl. When all the liquid has been added, beat on a high speed for 2 minutes until it is light and fluffy.
4. Divide the mixture evenly between the prepared tins and bake in the preheated oven for 25-30 minutes until golden brown.
5. While the cake is baking, place the sugar into a saucepan with 100ml of water and bring to the boil. Simmer for 2 minutes, then remove from the heat and stir in the rose water.
6. When the cakes are cooked, leave them to cool in the tins for 10 minutes, then liberally brush with the cooled rose syrup. Leave to cool completely.
7. To make the white chocolate decorations, melt the chocolate over a bowl of simmering water until smooth. Dip the strawberries into the chocolate and place them onto baking parchment to set. To make the shards, take a quarter of the remaining white chocolate and mix in the food colouring until it is one uniform colour, then transfer this mixture into a piping bag. Pour the rest of the white chocolate into a large, lined baking tray, then drizzle with the pink chocolate and scatter over dried strawberries and rose petals. Leave to set at room temperature for 30 minutes, then score 12 large triangles into it with a sharp knife. Chill until completely solid.
8. For the buttercream, beat the soft butter and icing sugar in a stand mixer until it clumps together. Add the Champagne, a few tablespoons at a time, until the icing loosens up and becomes fluffy. Beat on a high speed for 3-4 minutes to get air in.
9. To assemble, place the bottom layer of sponge onto a large plate. Spread the top with buttercream and 3 tbsp strawberry jam, repeat with the second layer of sponge, then add the third on top. Cover the whole cake with a thin layer of buttercream, then place in the fridge for 20 minutes to solidify. Then, using a large palette knife, coat the chilled cake with more buttercream to achieve a smooth, clean finish. Arrange the chocolate shards and strawberries on top, then sprinkle over some dried berries and rose petals before enjoying.
10. Any leftover icing can be kept in the fridge for up to a week to use for cupcakes or to fill macaroons.