1. Preheat oven to 180°C (350°F). Grease a 15×9 inch baking pan with softened butter or vegetable oil.

2. Melt the butter over low heat, then whisk in ½ chocolate bar until melted. (Alternatively, melt chocolate separately and combine with milk and coffee.)

3. Whisk in sugar until mixture is slightly grainy, about 2 minutes.

4. Add eggs, vanilla essence, and salt; whisk until smooth and thickened.

5. Slowly whisk in milk and brewed coffee.

6. In a separate bowl, mix flour, baking powder, and cocoa powder. Sift dry ingredients into wet mixture; whisk gently to combine. Avoid overmixing; finish within 3 minutes.

7. Pour batter into prepared pan. Bake for 14–17 minutes or until cake pulls away slightly from edges.

8. Cool the sponge cake completely before slicing.

Whipped Chocolate Ganache:

1. Use a double boiler method: place chocolate bar in a bowl over simmering water.

2. Add heavy cream and whisk over low heat until chocolate is melted and mixture is smooth. Avoid overheating.

3. Cool mixture for 30 minutes or refrigerate 10 minutes.

4. Whip ganache on low speed until thickened and fluffy.

Assembly:

1. Slice cooled sponge cake horizontally into two equal layers.

2. Spread whipped ganache evenly over the bottom layer. Optionally sprinkle toasted nuts and press gently into ganache.

3. Place the top layer on ganache to finish.

4. For decoration, melt additional chocolate and drizzle over top; sprinkle with remaining chopped nuts if desired.