In a mixing bowl, melt the white chocolate. Add the warm espresso and mix until well combined. Add the cold whipping cream then mix well. Cover with cling film, then set in the fridge for 2-3 hours. Whip until stiff before use.

Quickly boil the whipping cream in a saucepan, then remove it from heat. Pour the hot cream onto the chocolate to melt. Mix well till shiny. Add the cold whipping cream, then mix well. Cover with cling film, then set in the fridge for 2-3 hours. Whip until stiff before use.

Preheat oven to 170°C (338°F). Prepare a flat baking tray lined with parchment paper. Mix the oat milk and lemon juice, then set aside to thicken. Combine and sieve all dry ingredients. Make the vegan meringue recipe. Adjust the quantity based on what you need. Pour the liquid (oat milk and lemon mixture) to the dry ingredients. Add the melted butter, then mix well until a smooth batter forms. Gently fold the meringue into the joconde batter in two parts. Spread the batter (½ cm/ 0.2 in thick) onto the baking tray, then bake for 14 to 16 minutes or until lightly golden. Let the sponge cool down before cutting.

In a saucepan, boil water and sugar. Remove from heat, then mix in the coffee powder. Set aside.

Heat the whipping cream in a saucepan until it starts to boil. Remove from heat. Pour over the chocolate, then mix using a hand blender until smooth and shiny. Cover and keep in a warm place.

Cut three joconde sponge sheets into 24x24 cm (9.5x9.5 in) same size as the square metal mold. If using other mold sizes, cut the sponge sheets according to their shapes. Place one sponge sheet at the bottom of the mold and brush generously with the coffee syrup (1st layer). Spread the chocolate ganache evenly over the sponge (2nd layer). Place the second sponge layer moistened with coffee syrup (3rd layer), then spread half of the whipped coffee ganache over it (4th layer). Place the third sponge layer moistened with coffee syrup (5th layer), then spread the remaining whipped coffee ganache over it (6th layer). Spread the whipped chocolate ganache to finish off the 7th layer. Level the top layer using an offset spatula, then remove excess ganache on the sides. Freeze for at least 2-3 hours.

In a saucepan, boil the whipping cream and glucose. Remove from heat. Pour the hot cream over the dark chocolate. Mix with the hand blender to remove air bubbles and smoothen the glaze. Rewarm the glaze to about 40°C (105°F) before use. Place the frozen opera cake on a wire rack. Cover the top with a thin layer of warm dark chocolate glaze, then remove the metal cake mold. You may freeze it for 30 minutes to set the glaze before cutting.