Preheat oven to 350°. Place pitted prunes (soak in hot water for 30 minutes first, if you have time) in the bowl of a food processor. Add vanilla extract, and process until prunes are broken down into small pieces; set aside. Grease a 10-inch round cake pan. Place chocolate in a heatproof bowl, and microwave (in 1-minute intervals) until melted and smooth. Stir in butter and fold in the prune purée and ground hazelnuts. Beat eggs yolks with sugar with an electric mixer 4 minutes; fold into the chocolate mixture. Beat egg whites with salt with a clean whisk until stiff peaks form. Fold whites into the chocolate mixture in 3 batches. Pour batter into prepared pan, and smooth top. Bake 20 minutes, rotate pan, and continue baking 5–7 minutes. Let cool, cut into 12 slices, and serve.
My main criticism has to do with the writing of the recipe rather than the actual product. After baking the cake for a full thirty minutes (three minutes longer than the recipe's maximum time), it still jiggled like it was completely raw up to the outer edges. Since the recipe contained no information as what the cake should look like consistency-wise coming out of the oven, I then scoured the internet trying to find this same recipe with more details. The toothpick trick, I think, doesn't apply to flourless cakes - I'm not sure, because I've never actually made one before. I finally found a version that mentioned that the "center should feel soft." Well, that was an understatement, but we were at about 40 minutes by now and I was afraid it was going to be overdone. I took it out of the oven and let it cool.
The flavor is excellent - the prunes, chocolate, and hazelnuts are complex and wonderful - but the cake itself is severely underdone. All but the edges of the cake collapsed, and it has a pudding-y texture. The edges have a chewyness to them and are excellent...I only hope I can get the whole cake to turn out that way someday, after messing with the baking times more!
If anyone has any tips on how to tell if your flourless cake is done - please post!
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