Preheat your oven to 350°F (180°C) and line a 10x15 inch jelly roll pan with parchment paper.

In a medium bowl, sift together all-purpose flour, Dutch-processed cocoa powder, baking powder, salt, and instant coffee.

Whisk the egg yolks with half of the caster sugar until pale and thick, then mix in melted butter and vanilla extract.

In a separate bowl, whip the egg whites with the remaining sugar until stiff peaks form.

Gently fold in one-third of the whipped meringue into the yolk mixture, then add the remaining meringue and sifted dry ingredients, folding carefully.

Spread the batter evenly in the prepared pan and bake for 12-15 minutes.

Invert the baked cake onto a cocoa-dusted kitchen towel and roll it tightly while still warm.

Whip the heavy cream with powdered sugar until soft peaks form, then mix in mascarpone cheese until creamy.

Unroll the cooled cake, spread the filling, and roll it back up tightly. Chill for 30 minutes.

Melt chocolate, butter, brown sugar, and cream over low heat to make the chocolate sauce.

Slice the Swiss roll, drizzle with chocolate sauce, and serve immediately.