Preheat oven to 175C / 350F (not fan-assisted). Line the bottom 2 5-inch round cake tins with baking parchment (no need to grease or flour the tins).
Sift plain flour and corn flour together 3 times. Set aside.
Place butter and milk in a medium mixing bowl and melt them over a pot of simmering water or in a microwave (microwave at full power for 30 seconds. Give the mixture a stir, then microwave for 10 seconds, check the mixture and repeat until butter has melted). Set aside.
Heat a small pot of water and place a large mixing bowl of over - the bowl should fit snugly on top of the pot and the bottom of the bowl should be 1 inch away from the water surface. Remove the mixing bowl from the pot. Bring the water to a boil then turn the heat down to a simmer.
In the large mixing bowl, add in eggs and sugar. Whisk immediately with a wire whisk to mix them together. Place the mixing bowl over the pot of simmering water and whisk constantly until the mixture is warm like baby's milk (or until the sugar has melted). Remove the mixing bowl from the pot. You can turn off the heat as you don't need the pot of water anymore.
Change to an electric mixer and whisk the egg and sugar mixture on medium-high speed until thick and ribbony. This will take about 5 minutes. You should be able to draw an infinity symbol with the batter before the batter slowly sinks back into itself. Turn the electric mixer speed to low and add in vanilla and orange/lemon zest. Mix until incorporated.
Sift in 1/2 of the flour mixture and fold in with a rubber spatula until incorporated (never use an electric mixer for this step). Sift in the remaining flour mixture and fold until incorporated.
Pour 1/3 of the batter into the butter-milk mixture and fold until the butter-milk has been incorporated. Pour it back into the large mixing bowl and mix until the batter is homogenous.
Divide the batter between the 2 cake tins. Bake in the middle shelf for 18 to 20 minutes until a skewer inserted into the center comes out clean and the top of the cake springs back when touched lightly.
Cool the cake completely on a wire rack before using.
Combine sugar and water in a small pot. Bring to a boil and cook until all the sugar has dissolved. Remove from heat and let cool completely. Stir in the rum if using.
Chill a metal bowl and the beaters of an electric mixer in the refrigerator for 15 minutes.
Place water in a small heat-proof bowl. Sprinkle powdered gelatin on top of the water and set aside for 5 minutes. Place the bowl of gelatin in a pan of simmering water and heat until the gelatin has dissolved. Remove from heat and set aside.
Remove the chilled bowl and beaters from the refrigerator and add in the heavy cream and sugar. Whip the cream over high speed until soft peaks are formed. Add in maple syrup and vanilla and whip until incorporated. While the mixer is running, drizzle in the gelatin liquid until all the gelatin liquid has been added. Continue to whip until stiff peaks are formed. If the weather is warm, place the bowl of whipped cream over a bowl of ice water to keep the cream chilled.
Rinse and drain the strawberries then cut off the strawberry tops. Reserve 6 best-looking strawberries and chop up the rest into small pieces.
Run a spatula along the edges of the cake tins, turn the cake tins over to remove the cakes. Peel off and discard the parchment paper. Brush both sides of a cake layer with Syrup and place it on a cake board. Spread the cake layer with whipped cream and top the whipped cream with plenty of strawberry pieces. Cover the strawberry pieces with more whipped cream. Brush both sides of the second cake layer with Syrup then place it on top of the whipped cream. Spread the top and sides with whipped cream, reserving some for decoration.
Place the reserved whipped cream in a piping bag fitted with a star tip. Pipe rosettes all around the cake then decorate the cake with the reserved strawberries. Combine the strawberry jam and hot water together and brush it all over the strawberries for a glossy look.
The cake is best serve chilled, so chill the cake for about an hour before serving. Any leftover cake should be stored in a covered container in the refrigerator.
- If you want to bake a 7-inch cake, increase all the ingredients by 50%.- To make this cake in advance: make the cake and syrup one day before and store them, covered, in the refrigerator. Make the whipped cream and assemble the cake on the day itself.- Sponge cake recipe adapted from Japanese Cooking 101.