To make the cake, preheat the oven to 180℃ (170℃ fan)/350°F/gas mark 4. Line the base of a 23cm/9in cake tin with baking parchment and lightly grease. Place the self raising flour and hazelnuts in a food processor and blitz until the hazelnuts are very finely chopped.
Beat the butter and sugar together until very pale and fluffy. Lightly beat the eggs and gradually beat them into the mixture, beating well after each addition. Beat in the vanilla extract.
Carefully fold in the flour and hazelnuts until well combined. spoon into the prepared cake tin and level the top
Scatter the raspberries over the top of the cake.
To make the crumble topping, blitz the plain flour and butter in a food processor until the mixture resembles coarse breadcrumbs. Add the sugar and nuts and blitz very briefly to mix.
Remove the blade and sprinkle in a little cold water (about 1tbsp) , run a dinner knife through the mixture so that some of the crumbs stick together.
Scatter the crumble mixture over the raspberries and bake for about 1 hour until done, testing with a skewer which will come out clean when inserted into the centre of the cake when it is cooked.
Allow the cake to cool in the pan for about 10 minutes before transfer to a wire rack to cool.
Nutrition information is approximate and is meant as a guideline only.