Line a small loaf pan (approx. 20 x 10 cm) with parchment.
Melt base: In a heatproof bowl, gently melt the chocolate and butter over a bain marie (or in short microwave bursts). Stir until smooth, then let cool slightly.
Add sugar & espresso: Stir in the caster sugar and espresso powder until dissolved.
Add egg: Whisk in the beaten egg until glossy.Add dry ingredients:
Fold in the self-raising flour, salt, and seeds until just combined.
Caramel swirl: Pour half the batter into the loaf pan, drizzle over half the salted caramel, then add the remaining batter and swirl the rest of the caramel through the top.
Bake: Bake for 25 minutes, until set at the edges but slightly soft in the centre.
Finish: Cool in the tin, dust with icing sugar, slice into 2 generous squares, and serve with extra caramel sauce if desired.
Notes
you can omit the espresso powder and add in a teaspoon of vanilla for the children