Heat oven to 210'c, grease a muffin tray/cake tin and line with greaseproof paper or muffin cases.
In a medium bowl, beat Butter until creamy then beat in Castor sugar until pale and fluffy. Beat in Eggs, one at a time. Finally beat in Baking powder.
Mix in the crushed Walnut halves and fold in the Plain flour, Semi-skimmed milk and the Coffee granules dissolved in 10ml Boiling water. Spoon mix into muffin cases/cake tin.
For muffins bake for 25 - 30 minutes, for cake tin bake for 45-60, or until golden brown and not gooey in the middle. Allow to cool before removing from the tray.
Melt the butter and sieve in the Icing sugar, melt the Coffee granules with the Boiling water and Vanilla Essence and combine all of the ingredients. Stir until all combined, if too thin sieve in extra Icing sugar. Apply to muffins once they are cooled.
Don't make this recipe! stodgy, nasty outcome. I suspect that if you reduce the sugar by 100g, and reduce the flour by 250g, it wouldn't be too bed - but as it is , it is truly the worst recipe I have ever seen in the public domain!!! AVOID!!!