Preheat oven to 180 degrees C. Grease and flour a 23cm round cake tin and line bottom with baking paper.
In a large bowl stir together flour, 3/4 cup sugar, cocoa, instant coffee, bicarb soda and salt. Beat in softened butter, sour cream, egg and 1/2 teaspoon vanilla. Beat on medium speed for 3 minutes. Pour batter into prepared tin.
Bake in the preheated oven for 30 to 35 minutes, or until a skewer inserted into the centre of the cake comes out clean. Cool for 10 minutes in tin then turn out onto a wire rack. Gently peel off baking paper. Cool completely.
In a small saucepan combine cream, 1/4 cup sugar, 1 tablespoon butter, golden syrup and chocolate chips. Cook over medium heat, stirring constantly, until mixture boils. Continue to cook while stirring for 5 minutes. Remove from heat and cool 10 minutes. Stir in nuts and vanilla.
Place cake on serving plate. Pour glaze evenly over cake, allowing some to run down sides. Arrange pecan halves on top. Refrigerate until glaze is firm, about 1 hour.