Preheat the oven to 180c 350f
Grease the tin with non stick baking spray, if you don't have any spray i use this method to ensure it will be non stickUsing a brush, grease the tin with melted butter ensuring it gets in to all the edges and then sift in some flour to coat the tin, shake it around and tap the tin upside down over the sink to remove any excess flour and place the tin in the fridge to harden the butter.
Mash the bananas in a bowl using a fork. Add the vanilla and place to one side,
Place the softened butter and sugar in a bowl and whisk for at least 5 minutes until it is very pale and creamy. it may take longer. I use an electric stand mixer, but a hand held electric whisk will work too.
Add the eggs one at a time, beating for a minute, then stop and use a spatula to scrape the bowl before adding the next egg.
Then add the creme fraiche and mashed bananas and mix in.
Sift in the flour, salt and mix together with the wet ingredients. (if using plain flour rather than self raising flour, ensure you sift the baking powder and flour together first)
Add the chopped chocolate and hazelnuts and mix in.
Tip mixture into the prepared tin, tap to level out and ensure it is filled properly. Bake in the centre of the oven for about 50 minutes. It is baked when a knife inserted comes out clean
Removing from the bundt tin in one piece. My tip for this is to let cool in the tin for 15 minutes, then turn out to cool further on a wire cooling rack.