The way they made it low-fat was to substitute pureed prunes for the butter. Well, it looked ok when I put it in the oven, smelt chocolatey as it was cooking. Took it out, took one bite. Prunes. All you can taste are the flipping prunes. Tried a bite from a different bit to see if I was unlucky. Nope. This is a prune brownie. All evidence of the big bar of dark chocolate that went in it has evaporated. Not only that, but the added brownie stickiness means that the prune taste clings. I ended up cleaning my teeth because the taste still hadn't disappeared after about 15 minutes. Ok, so perhaps if you really, really like prunes this is the thing for you, but then again it seems a waste of a bar of chocolate.
In conclusion: do not substitute prunes for butter.
(It is lurking in the fridge. I'm going to see if anyone at work really likes prunes)
ETA: Recipe requested for avoidance purposes.
140g melted dark chocolate
Tin of prunes in fruit juice, drained
100g wholemeal breadcrumbs
1 whole egg & 2 egg whites (I used linseed squodge)
140g golden caster sugar
1/2tsp vanilla extract
Whuzz all ingredients together. Bake in greased cake tin for c30 mins. Cool. Taste. Regret loss of chocolate bar.