160g (1/2 cup) chocolate hazelnut spread
180g unsalted butter, at room temperature, coarsely chopped
270g (1 1/4 cups) caster sugar
1 teaspoon vanilla extract
3 eggs, at room temperature
170g (2/3 cup) sour cream
225g (1 1/2 cups) plain flour
1 teaspoon baking powder
2 tablespoons white sugar
70g (1/2 cup) chopped pecans
125g dark chocolate, coarsely chopped
60ml (1/4 cup) pouring cream
60ml (1/4 cup) milk
Preheat oven to 160°C. Brush a round 20cm (base measurement) springform pan with melted butter. Line base with non-stick baking paper. Place the chocolate spread in a bowl and stir until softened.
Use an electric beater to beat the butter, sugar and vanilla in a bowl for 5 minutes or until pale and creamy. Add the eggs, 1 at a time, beating well after each addition. Beat in sour cream. Sift flour and baking powder in a bowl. Fold flour mixture into butter mixture.
Spread half the butter mixture into the pan. Top the butter mixture with spoonfuls of chocolate spread. Use a knife to create a swirled effect. Repeat with remaining butter mixture and chocolate spread. Top with sugar and pecans. Bake for 1 hour 10 minutes or until a skewer inserted into centre comes out clean. Set aside for 5 minutes to cool slightly.
Meanwhile, combine chocolate, cream and milk in a saucepan over low heat. Cook, stirring, for 3 minutes or until smooth. Set aside to cool slightly. Serve with the cake.