Preheat oven to 160C. Grease and line three 20 cm round cake tins. In a large bowl, add flour, baking powder, bicarbonate of soda and salt, whisk to combine. In a separate bowl, whisk together the sour cream, eggs and sugar. Add the oil, buttermilk, and vanilla, whisk to combine. Add the dry ingredients and fold through until just combined. Add the raspberries and fold through, being careful not to break them up too much. Add the raspberry jam and gently swirl through briefly, without fully incorporating into the mixture. Divide the batter between the three cake tins and smooth out. Bake for 30-35 minutes, until a skewer inserted into the centre of one of the cakes comes out clean. Cool in tins for ten minutes before transferring to a wire rack. Let the cakes cool completely before assembling.

To make the buttercream, first melt the white chocolate in 10 second bursts in the microwave, stirring at each interval until smooth, set aside to cool slightly. Using an electric mixer, beat butter and vanilla until smooth and light. Add half the icing sugar and beat until combined, follow with remaining icing sugar and beat until combined. Add the melted white chocolate and beat until incorporated. Gently fold the raspberry jam into the buttercream, until just swirled through.

To assemble, trim the top of the cakes to make them level. Place one cake layer on a serving plate. Spread ¼ of the buttercream over the cake. Layer with the second cake layer and spread with another ¼ of the buttercream. Complete with final cake layer, placing the top side face down. Spread and swirl the remaining buttercream over the top and sides of the cake. Decorate with whole and torn fresh raspberries. Chill for at 30 minutes before slicing.