Preheat oven to 180°C (160°C fan forced). Grease and line a 20cm deep round cake pan. Line the base with baking paper.
Beat cake mix, eggs, orange juice, yoghurt and butter in a medium bowl with electric beaters on low speed for 30 seconds, then on medium speed for 2 minutes. Pour mixture into pan.
Bake for 50 minutes, or until a skewer inserted into the centre comes out clean. Cool for 10 minutes in pan, and then gently remove from pan onto a wire rack.
Line 2 shallow 30cmx20cm rectangular baking trays with a sheet of baking paper. Spread half a tub of chocolate frosting over the paper of each tray, leaving a small border around the edges. Scatter over almonds. Bake undisturbed for 20 minutes. The frosting will bubble up over the almonds and create a toffee. Remove from the oven and allow to cool on the tray.
Blitz half the toffee in a food processor to small pieces and break remaining toffee into shards.
Slice cake in half and fill with mascarpone and sandwich together. Spread vanilla frosting over top and sides of cake. Press crushed toffee onto sides and shards on top of cake.