Preheat the oven to 180°C (160°C fan). Line two baking trays with parchment and lightly grease. Draw 6 small circles around 18 cm in diameter as guides for even sponge layers. Set aside and move to the next step.

In a large bowl, beat the egg yolks with half the caster sugar until pale and thick. The mixture should leave a ribbon trail when lifted, which ensures the sponge will remain light. Continue to the next step.

In a separate clean bowl, whisk the egg whites with a pinch of salt until soft peaks form. Gradually add the remaining sugar and whisk until glossy stiff peaks develop. This structure gives the sponge its airy texture. Proceed to folding.

Gently fold the egg whites into the yolk mixture in stages, followed by the sifted flour and vanilla extract. Use a light hand to avoid knocking out air. The batter should remain airy as you move to shaping the layers.

Spread a thin, even layer of batter within each marked circle. Bake for 6 to 8 minutes until lightly golden. Remove carefully and cool on a wire rack. Repeat until you have six uniform layers, then proceed to the buttercream.

Beat the softened butter with icing sugar until smooth and pale. Add the cooled melted chocolate, vanilla, and salt. Continue beating until silky and spreadable. Taste and adjust sweetness if needed before assembling.

Place one sponge layer on a serving board and spread a thin layer of buttercream evenly. Repeat with remaining layers, stacking carefully to maintain straight sides. Leave the top layer plain for caramel and move to the next step.

In a small saucepan, heat caster sugar with lemon juice over medium heat until it melts into a deep amber caramel. Work quickly as it sets fast. Pour over the top sponge layer and spread thinly. Continue to shaping.

While the caramel is still slightly pliable, lightly score and cut it into wedges using a buttered knife. This prevents cracking later. Allow it to cool fully before placing the pieces on top of the cake.

Arrange the caramel wedges decoratively on the cake. Slice carefully with a sharp knife to preserve the layers. Dobos Torta is best served at room temperature with coffee, allowing the buttercream to soften slightly for full flavour.