Preheat the oven to 180C/Gas4 and grease a 25cm bundt tin or a deep 23cm round cake tin, with a little butter
Dissolve the coffee in 2 tablespoons of boiling water, stir in the vanilla and oil and set aside; whiz the hazelnuts with half the flour in a food processor until finely ground
Put the butter and sugars in a large bowl and whisk together until pale and fluffy; beat in the eggs, one at a time, adding a spoonful of flour between eggs to avoid curdling; in another bowl, mix the rest of the flour, the hazelnut flour mixture, baking powder and salt; stir in half these dry ingredients, followed by the coffee mixture and half the buttermilk; repeat – add the remaining dry stuff and the last of the buttermilk
Pour the mixture into the greased tin, then bake on a middle shelf for 55 minutes or one hour, until a skewer comes out clean; cool in the tin for 15 minutes, then turn out onto a wire rack; leave to cool completely
To make the glaze, sit the wire rack with your cake on, over a clean tray to catch extra icing; put the Nutella, syrup, butter and cream in a small pan and melt together over a low heat; once runny, but not boiling, quickly transfer to a jug; pour the glaze over the whole cake; allow to set for 15 minutes
12 servings