Melted butter, to grease
90g plain flour
70g brown sugar
70g unsalted butter, frozen, coarsely grated
Extra 175g unsalted butter, chopped, softened
175g caster sugar
2 tsp vanilla extract
1/4 cup strong black coffee, chilled
75g sour cream
125g hazelnut meal
130g self-raising flour
1/2 tsp baking powder
1 1/2 cups mini dark chocolate chips
Double cream, to serve
Preheat oven to 160°C. Grease a 24cm-angel food cake tin. Line the base, side and middle with baking paper. Combine plain flour, brown sugar and grated butter in a bowl and rub using fingertips to form a crumble. Set aside.
Put softened butter and caster sugar in the bowl of an electric mixer and beat with paddle attachment on medium speed for 5 minutes or until light and fluffy. Beat in eggs, 1 at a time, beating well after each addition. Fold in vanilla, coffee, sour cream and hazelnut meal. Sift in self-raising flour and baking powder, then stir until smooth.
Spread 1/2 the batter into prepared tin. Top with 1/2 the crumble and 1/2 cup of the chocolate chips. Finish with remaining batter, crumble and chocolate chips. Bake for 50 minutes or until a skewer can be inserted and removed cleanly. Serve with double cream.