Preheat the oven to 350 degrees. Put 20 paper baking cases in 2 muffin pans.
Put the coffee granules, butter, sugar, honey, and water in a pan and heat gently, stirring, until the sugar has dissolved. Bring to a boil, then reduce the heat and let simmer for 5 minutes. Pour into a large heatproof bowl and let cool.
When the mixture has cooled, add flour and cocoa. Dissolve baking soda in the milk, then add to the mixture with the egg and beat together until smooth. Spoon the batter into paper cases.
Bake the cupcakes in the preheated over for 15-20 minutes, or until well risen and firm to the touch. Transfer to a wire rack to cool.
For frosting, beat all ingredients, except nuts with a mixer until fluffy. Spread frosting to each cooled cake, and top with nuts.