Delightfully tangy rhubarb takes this layered lemon sponge cake
to new heights. What could possibly sit better on a table set for
250 gmbutter, softened400 gmcaster sugar Finelygrated rind of 3 lemons, juice of 1½ 5eggs400 gm (2 cups)plain flour5 tspbaking powder150 mlmilk450 gmsour cream60 gmpure icing sugarWhipped lemon curd5egg yolks150 mllemon juice110 gm (½ cup)caster sugar1½titanium-strength gelatine leaves, softened in cold water for 5 minutes150 gmbutter, softenedRoast rhubarb500 gmrhubarb (about 1½ bunches), trimmed, cut into 5cm lengths300 gmcaster sugar120 mldessert wineJuiceof 1 orange and 1 lemonScrapedseeds of 1 vanilla bean
For whipped lemon curd, whisk yolks, lemon juice and sugar in a heatproof bowl over a saucepan of simmering water until pale and very fluffy (4-5 minutes). Squeeze excess water from gelatine and whisk into yolk mixture. Remove from heat and whisk in butter, a little at a time, until combined. Refrigerate in a sterile container until chilled (3-4 hours).
For roast rhubarb, preheat oven to 200C. Toss rhubarb, sugar, dessert wine, citrus juices and vanilla seeds in a bowl to coat well, place in a roasting pan large enough to fit rhubarb in a single layer and roast until rhubarb is just tender (8-10 minutes). Set aside to cool completely.
Reduce oven to 170C. Beat butter, sugar and lemon rind in an electric mixer until pale and fluffy (3-4 minutes). Add eggs one at a time and beat well after each addition. Beat in half the flour and half the baking powder to just combine. Whisk milk, lemon juice and 150gm sour cream in a separate bowl until smooth, then beat into batter. Beat in remaining flour and baking powder to just combine. Divide between two 22cm-diameter cake tins that have been buttered and bases lined with baking paper, and smooth tops with a palette knife. Bake, swapping placement of tins halfway through cooking, until golden and the centres spring back when lightly pressed (45-50 minutes). Cool slightly in tins, turn onto wire racks and cool completely, then trim tops flat with a knife.
Whisk lemon curd in a bowl until smooth, spread over the top of one cake, then sandwich with second cake. Whisk icing sugar and remaining sour cream until thick, spoon on top of cake, top with a little roast rhubarb and serve with remaining rhubarb.