Chocolate Caramel Swiss Roll

PREPARE THE TIN
Preheat the oven to 190°C (375°F / Gas 5). Line a Swiss roll tin (33 × 23 cm / 13 × 9 inch) with baking parchment, smoothing out all creases. Lay a second sheet of baking parchment on your work surface and dust it generously with caster sugar - you will need this ready when the sponge comes out of the oven.

MAKE THE CHOCOLATE SPONGE
In a large heatproof bowl set over a pan of barely simmering water, whisk the eggs and caster sugar together until the sugar has dissolved and the mixture is warm to the touch (about 40°C). Remove from the heat and whisk on high speed with an electric mixer for 5–7 minutes until pale, thick, and tripled in volume - the ribbon stage. Sift the flour, cocoa powder, and salt together. Fold gently into the egg mixture in two additions using a large metal spoon with light, sweeping strokes. Drizzle the cooled melted butter down the side of the bowl and fold in until just incorporated. Do not overmix.

BAKE THE SPONGE
Pour the batter into the prepared tin and spread evenly to the corners with an offset spatula. The batter should produce a thin, even sheet of approximately 7–8 mm depth - a too-thick sponge will not roll cleanly. Bake for 12–14 minutes until the sponge springs back when touched and has just begun to shrink from the edges. Do not overbake - a dry sponge will crack when rolled.

ROLL WHILE WARM
Immediately upon removing from the oven, invert the sponge onto the sugar-dusted parchment and peel away the lining parchment. Working quickly while the sponge is still hot, use the parchment beneath to roll the sponge up tightly from the short end, with the parchment inside to prevent sticking. Hold the roll in position for 30–60 seconds, then leave to cool completely on a wire rack, still in its rolled shape. Rolling the sponge while still pliable trains a tight spiral into the structure - a cold sponge will crack. Do not attempt to fill until completely cool.

MAKE THE THICK CARAMEL
Place the sugar in a medium heavy-based saucepan. Cook over medium-high heat, swirling the pan (not stirring) until the sugar melts to a deep amber caramel (approximately 170°C / 340°F). Remove from the heat. Carefully pour in the warm cream - it will bubble vigorously - and whisk until smooth. Add the cold cubed butter and salt, whisking until fully incorporated. Transfer to a bowl and leave to cool until thickened but still spreadable, about 20–30 minutes. The caramel should hold a soft peak when dolloped. If too runny, refrigerate briefly.

MAKE THE MILK CHOCOLATE COFFEE GANACHE
Place the finely chopped milk chocolate in a heatproof bowl. Heat the cream until it just begins to simmer - do not boil. Dissolve the espresso powder in the hot cream, then pour over the chocolate. Leave to stand for 2 minutes, then stir from the centre outward until smooth and glossy. Add the butter and stir until incorporated. Leave to cool at room temperature until thickened to a spreadable consistency, about 30–45 minutes. Refrigerate briefly and stir if needed.

FILL AND RE-ROLL
Unroll the cooled sponge carefully - it should uncurl without cracking. Spread the caramel evenly over the surface, leaving a 1 cm border along the far short edge to prevent filling being squeezed out during rolling. Spread the milk chocolate coffee ganache over the caramel in an even layer, using an offset spatula for both. Re-roll the sponge tightly, this time without the parchment inside, using the parchment underneath to keep the roll even and tight. Press gently as you reach the end to seal. Sit the roll seam-side down.

CHILL AND SERVE
Wrap the finished roll tightly in parchment, then in cling film. Refrigerate for at least 30 minutes, ideally 1 hour, before serving - chilling sets the ganache and holds the spiral in shape. Trim both ends with a sharp serrated knife to reveal the spiral cross-section. Dust with cocoa powder or icing sugar if desired. Slice with a sharp knife, wiping the blade between cuts for clean slices. Serve chilled or at cool room temperature.