Preheat your oven to 180°C/ 160°C fan oven/ Gas Mark 4. Grease and line 4x 7 inch cake tins. In a large bowl whisk together the melted butter and oil until blended. Add the water then whisk again until well blended.
In a jug beat together the eggs, vanilla and soured cream. Add to the butter mix and whisk again.
In a separate bowl mix together the flour, cocoa powder, caster sugar, light brown sugar and the bicarbonate of soda and baking powder. Add to the wet ingredients and whisk until well mixed.
Divide the cake batter between the cake tins and bake in the oven for 25-30 minutes until cooked. To test if the cake is cooked insert a skewer and if it comes out clean then the cakes are ready. Take the cakes out of the oven and cool in their tins for 30 minutes then remove from the tins and cool completely.
To make the white chocolate and vanilla bean buttercream filling, melt the white chocolate in a glass bowl in the microwave in 20 second bursts, stirring in between until melted. Leave to cool for 10-15 minutes until room temperature but still fluid. Put the butter into a large bowl and beat with an electric whisk or freestanding mixer until light and fluffy.
Sift in the icing sugar then add the vanilla bean paste and beat again until well incorporated. Add the melted white chocolate and beat together for a couple of minutes until light and fluffy in texture.
To make the vanilla swiss meringue buttercream coating, fill a pan with water so it is 1/3 full and bring to the boil. In a large heatproof bowl or the bowl of a freestanding mixer combine the egg whites, sugar and salt. Put the bowl over the pan of water (this is called a bain marie) making sure the bottom of the bowl does not touch the water and whisk the egg whites and sugar together for a minute or two until the mixture is frothy, the sugar has dissolved and it is warm to the touch.
Remove from the pan and whisk with the freestanding mixer or a hand held electric whisk until the mixture forms medium soft peaks and is cooled to room temperature. With the mixer running on medium high gradually add the softened butter a table spoon at a time until it is all incorporated and beat for a few minutes until light in colour. The mixture may look like it is curdling but keep whisking and it will eventually combine to make a smooth buttercream.
To fill the cakes – level each cake with a bread knife. Place your first layer on a cake board slightly wider than your cake then add a layer of white chocolate vanilla bean buttercream. Pipe a ring about 1inch thick of the buttercream around the edge of the cake then fill the ring with half the raspberry jam.
Add the second layer of cake and repeat the filling process. Add the third layer of cake then take the remaining white chocolate vanilla buttercream and spread a thin crumb coat all over the cake. Put in the fridge to chill and set for 1 hour.
Once the crumb coat has set, remove from the fridge and add a layer of the swiss meringue buttercream just to the middle third of the cake.
Mix the glamour and sparkle sprinkles with some of the red and green bright and bold sprinkles. Alternatively, just use the glamour and sparkle sprinkles. Take the sprinkles and using your palm, pat onto the band of buttercream to form a thick layer of sprinkles.
Put in the fridge for 30 minutes to firm up. Remove from the fridge and then add a thick layer of the swiss meringue buttercream to the top and remaining top and bottom thirds of the cake up to the edge of where the sprinkles are.
Smooth with a palette knife or cake smoother, leaving the edge of the buttercream near the sprinkles rough and uneven.
Take the edible gold paint and paint onto the rough edge of the buttercream next to the sprinkles. Put the remainder of the swiss meringue buttercream in a piping bag fitted with the closed star nozzle and pipe 8x rosettes or ‘trees’ onto the top of the cake. Scatter with some more sprinkles.