1.Preheat oven to 180°C. Grease two deep 22cm-round cake pans; line bases with baking paper.
2.Beat butter, sugar and egg yolks in medium bowl with electric mixer until light and fluffy. Using wooden spoon, stir in combined sifted flour and cocoa powder, then combined buttermilk and sour cream. Divide mixture between pans.
3.Beat egg whites in small bowl with electric mixer until soft peaks form; gradually add extra sugar, 1 tablespoon at a time, beating until sugar dissolves between additions. Divide meringue mixture evenly over cake mixture in pans; using metal spatula, spread meringue so cake mixture is completely covered. Sprinkle nuts over the meringue on one of the cakes.
4.Bake for 10 minutes. Cover pans loosely with foil; bake about 20 minutes. Discard foil; stand cakes in pans 5 minutes, before turning onto wire racks. Quickly and carefully turn cakes top-side up to cool.
5.Beat cream and icing sugar in small bowl with electric mixer until firm peaks form. Place cake without almonds on serving plate; spread cream over top, sprinkle evenly with raspberries, top with remaining cake.
These cakes are quite fragile so, after turning cakes out of the pans, it’s best to use two wire racks to turn them top-side up. If you have two 22cm springform tins, use them for baking these cakes then there’ll be no need to turn the cakes. This cake is best made on the day of serving; store in an airtight container in the refrigerator.