Adjust the oven rack to middle position. Preheat the oven to 180°C. Butter two 22 cm cake pans and line the bases with baking paper. Beat the eggs and oil together on high speed with an electric mixer or hand beater until well blended. Add the coffee and beat on high speed for 1 minute. Add Cake Mix and fold in with a spatula until just blended. Divide the mixture evenly between the two pans. Bake for 35-40 minutes. Leave the cakes to cool in the pans for 10 minutes. Turn out onto a cooling rack and leave until cold. Cut each cake through the middle to form two layers. When the inside is cold the cakes can be sandwiched together with the mousse.
Make up Mousse according to pack instructions using only 1 cup of water. Divide the mousse mixture roughly into three. Spread one third of the mousse on the cut side of one of the bottom layers. Smooth right to the edges of the cake with a palate knife. Place the next layer on top. Proceed in this way until all the mousse and three of the four cake layers have been used. The top layer of cake must be placed best side up.
To stabilize the cake and ensure a neat shape, wrap a double layer of wax or greaseproof paper around the sides of the cake. Secure tightly with clothes pegs and refrigerate overnight.
Serve on a cake plate sprinkled with rose petals, dusted with cocoa powder or icing sugar.