Put the dark chocolate and butter in a large microwave-safe bowl. Microwave in 30-second bursts, stirring between each burst until melted. Avoid overcooking as this can negatively affect the chocolate.
Add the caster sugar. Stir through with a manual whisk - I say stir as you don’t want to add air but a whisk is still the best tool as it distributes everything quickly.
Add the eggs and vanilla. Stir with the whisk again.
Put the flour through a sieve into the bowl. Stir to combine.
Tip in the chopped Daim bars and fold through.
Assemble
Pour the brownie batter into your prepared tin and level off.
Drizzle with the caramel and swirl a little with the handle end of a spoon.
Bake for approximately 30-35 minutes until a skewer pushed into the centre comes out with sticky crumbs (bear in mind you may hit pieces of Daim bar, so test in 2-3 places).
Allow to cool in the tin, then chill overnight to make them easy to slice.
Slide onto a serving board and slice in 12 pieces (in a pattern of 3 by 4).