Blitz the hazelnuts in a food processor until you have a smooth, thick paste.
Place the butter, vanilla, salt and kirsch in a bowl along with the hazelnut paste. Beat using the whisk on a hand mixer. Sieve in the icing sugar, continue to beat until the mixture is light and creamy. Whisk in the eggs one at a time. Combine the hazelnuts, flour and baking powder, stir into the mixture. Transfer the cake batter to the prepared tin.
Approx. 30 mins. in the lower half of an oven preheated to 180°C. Remove from the oven, allow to cool slightly in the tin, remove the tin frame, slide onto a cooling rack and leave to cool completely.