Grease and line a 20 cm round cake tin with greaseproof paper.
Melt butter, golden syrup, chocolate and warm water over a pan of simmering water. Cool slightly. Preheat oven to 170°C.
Put sifted dry ingredients into a large mixing bowl and stir in sugar, Nestle cream, vanilla essence, beaten eggs and oil to mix. Gradually pour in the chocolate mixture. Mix well with a wooden spoon. Fold in the chopped walnuts.
Turn batter into prepared cake tin and bake for about 40-50 minutes or until skewer inserted into the centre of the cake comes out clean.