Well i know this subject has been beautifully covered before, but i thought i could share my experience with you. Last week end i made Pierre Hermé's Nutella Tart for my sister's birthday. The pastry and filling are straightforward and turned out perfectly. I made a 20cm tart, so there definitely was some ganache (can you really call a mix of butter/chocolate a ganache?) left. I also used less hazelnuts and didn't toast them before baking as i reckon 11 minutes in the oven would allow them to developp the nice nutty flavour you look after when roasting them first. And as it was for my little sister - who doesn't like the bitterness of high cocoa percentage chocolate - i used a 60% cocoa solide chocolate for the ganache. Here are the results (sorry for the number of pictures, i couldn't resolve to post just one!) The finished tart Nice detail And the last one! The tart was delicious - but then hazelnut and chocolate is my favourite combo. I love the way the subbtle 'almondiness' of the tart crust highlighted the nuttiness of the nutella.