1. For the steeped Madeira (to be used as a flavor-builder for the other tiramisu components), heat the Madeira on low heat with the tea bags and lemon peel and let steep on low heat for about 15 minutes, to extract the flavor. Remove the tea bags and lemon peel, stir in the vanilla and set aside to cool.
2. For the syrup, whisk the hot tea with the sugar until the sugar dissolves and then stir in 20ml of the steeped Madeira. Set this aside until ready to assemble.
3. For the cream, whip the cream with the skim milk powder until the cream holds a soft peak when the beaters are lifted. Stir in the sugar and 40ml of the steeped Madeira. Chill until ready to assemble.
4. For the filling, beat the mascarpone gently to soften and then fold in half of the whipped cream in two additions. It may take folding this quite vigorously, using a whisk (depending on the brand of the mascarpone and how firm or soft it is). Don’t worry if the cream deflates a little when folding – this is factored in. Set aside.
5. Place a saucepot with 25 mm of water over medium heat until simmering. Whisk the egg yolks, sugar and 65ml of the steeped Madeira in a metal bowl and place this over the pot of simmering water, whisking constantly until the mixture has more than doubled in volume and holds a “ribbon” on the surface when the whisk is lifted. Remove from the heat and add the chocolate, whisking until melted. Whisk in a third of the mascarpone mixture until smooth (again, if it deflates a little, that is alright) and then fold in the remaining two-thirds of the mascarpone cream. Set aside or chill until ready to assemble.
6. To assemble, slice the Genoise cake in half horizontally. Place a 23-cm springform pan ring on top of a platter or cake board and place one of the cake layers in the bottom (there will be a 25mm gap between the cake and pan). Arrange the lady finger biscuits upright around the inside edge of the pan** (the cake layer will help secure them in place). Brush half of the syrup over the sponge cake and top with half of the filling, spreading evenly. Top this with the second cake layer, brush with the remaining syrup and top with the remaining filling, spreading. Top this with remaining whipped cream, spread evenly and top with a little grating of milk chocolate. Chill for at least 4 hours before serving.
To serving, unlatch and remove the springform ring from the cake, and cut into slices.
**If the lady fingers are taller than the height of the springform cake ring, you can trim a little from one end of each biscuit, making a flat end to place at the bottom when arranging.
To make the Genoise Sponge Cake
1. Preheat the oven to 160 °C. Line the bottom of a 23 cm springform pan with parchment paper, but do not grease the pan or line the sides with parchment.
2. Using beaters or a stand mixer fitted with a whisk attachment, whip the eggs and sugar on high speed until they are almost white in colour, more than triple in volume and hold a ribbon when the beaters are lifted, about 5 minutes.
3. Sift the flour and salt and, still on medium speed, add the flour to the egg mixture. Spoon about a cup of the batter into a bowl, and stir in the melted butter and vanilla. Add this all back to the full batter and stir by hand until blended. Pour the batter into the prepared pan and bake for about 40 minutes, until the centre of the cake springs back when gently pressed. Cool the cake completely in the pan.
4. To extract the cake from the pan, run a palette knife around the inside edge of the pan to loosen to cake, then unlatch the ring and peel away the parchment paper from the bottom.
Genoise sponge can be made a day ahead and wrapped in plastic wrap (do not refrigerate), or frozen until and thawed when needed.