Preheat the oven to 180°C (160°C for fan assisted ovens)/Gas Mark 4. Lightly grease a 15cm round deep cake tin and a 20cm round deep cake tin and line the bases with baking paper.
Add each cake mixture to separate mixing bowls. Stir 90ml oil, 180ml water and 3 eggs into each cake mixture, then whisk (by hand or electric mixer) for 2-3 minutes until smooth and creamy. Spoon 1 whole cake mixture, plus a quarter of the second bowl of mixture (about 205g), into the 20cm cake tin and gently level the surface. Spoon the remaining mixture into the 15cm cake tin and gently level the surface.
Bake the large cake for 50-55 minutes and the small cake for 45-50 minutes, or until a round bladed knife inserted into the centre of each cake comes out clean. Cool a little before turning out onto a wire rack to cool completely. Remove the baking paper.
To assemble, first trim the tops of the cakes with a serrated knife so they are flat. Place cut-side down on a cake board and cut each cake horizontally into 3 even layers (see Tip). Sandwich the layers of both cakes back together with just under 1½ tubs of the icing. Chill both cakes for 30 minutes.
Place the large cake on a cake board or stand and using a small palette knife, spread just over half the remaining icing over the top and sides of the cake in a smooth, thin layer. You should be able to see the layers of cake through the icing to give a ‘barely there’ effect.
Gently centre the small cake on top of the large iced cake and, using the rest of the icing, cover the cake in the same way, making sure to fill in any gaps between the 2 cakes with icing. Chill the tiered cake for 30 minutes before serving.
Just before serving, arrange the berries, redcurrants (if using) and flowers on top and around the sides of the cake. Dust lightly with icing sugar.
- To cut each cake into 3 equal horizontal slices, use a ruler as a guide and mark the side of the cake into three equal layers at frequent intervals with the tip of a knife. Hold the cake firmly in place with the palm of one hand and use a large serrated knife to cut horizontally through each layer, following the knife marks.
- To get smooth sides when icing the cakes, hold the palette knife blade against the side of the cake and drag it round in one continuous motion. To make it easier, put the cake board or stand on a cake turntable, if you have one.
- If you only have a small fridge, ice the cakes separately and keep chilled in the fridge until required, then assemble just before serving. Save a little bit of icing to fill in any gaps between the 2 cakes using the tip of a small palette knife.