Prepare the batter – Whisk oil, powdered sugar, and curd until smooth. Add vanilla essence.
Mix dry ingredients – Sift flour, cornflour, cocoa powder, baking powder, and baking soda. Fold gently into the wet mixture, adding milk for a smooth consistency.
Bake the cake – Pour into a greased tin and bake at 180°C (350°F) for 25–30 minutes, or until a toothpick inserted comes out clean. Cool completely.
Make the truffle ganache – Heat cream and butter until just simmering. Pour over chopped dark chocolate, let sit, then whisk into a glossy ganache. Chill slightly.
Slice and layer – Cut the cooled cake into even layers. Place the first layer on a plate, spread ganache, then repeat with remaining layers.
Cover and chill – Coat the entire cake with ganache, smooth the surface, and refrigerate 4–6 hours (or overnight) to set.
Finish and serve – Pour any extra ganache over the chilled cake for a glossy finish. Garnish with nuts, sprinkles, or chocolate shavings if desired.