Preheat oven to 180 degrees. Mix flour, sugar and baking powder in a bowl and beat in the butter until the mixture is creamed. Now whisk together the cocoa, sour cream, vanilla and eggs and beat into the creamed mixture. Pour cake batter into greased/lined baking pan and bake for about 25-35 minutes or until a skewer comes out clean. Let cakes cool before icing. For the icing, melt butter and chocolate over a double boiler or in the microwave and let it cool for a few minutes (be careful not to burn it). Meanwhile, sift icing sugar in another bowl. Add honey/golden syrup to chocolate mixture followed by the sour cream and vanilla. Mix well and then whisk in the icing sugar. If you want the icing to be runnier, add a few drops of boiling water or if you want it thicker, add more icing sugar. Spread icing onto cake with a palette knife and decorate as desired.
INFO & TIPS
Make sure that eggs and sour cream are at room temperature. Icing shouldn't be too thick or too runny.