Preheat your oven to 180°C/160°C(fan)/350°f/Gas 4.
Cream 225 g Butter and 225 g Dark brown sugar together until fluffy.
Dissolve 2 tablespoon Instant coffee in 2 tablespoon warm water and mix into the butter/sugar.
Mix in 4 Eggs.
Carefully fold in 225 g Self-raising flour and then fold in 60 g Walnuts.
Grease and line the loaf tin. Pour the cake batter into the tin. Cook for 40-45 minutes, until a skewer or toothpick comes out clean. Remove from the oven and allow to cool for 5 minutes. Remove from the tin and put onto a wire rack. Allow to cool completely.
To make the icing:
Cream together 100 g Butter and 200 g Icing sugar, until light and fluffy.
Dissolve 2 tablespoon Instant coffee in 2 tablespoon warm water and mix into the buttercream, along with 2 tablespoon Whole milk.
Spread the buttercream over the cooled cake and decorate with more Walnuts (optional).
Notes
If your cake starts to look like it is burning on top, cover it in foil and continue cooking until a skewer comes out clean.
Add some chocolate chips to the mixture for a delicious chocolate coffee combination.
To ensure that your cake is cooked all the way through and doesn't burn either, use an oven thermometer to make sure it gets to the correct temperature for the recipe.
Don't over mix the batter once you add the flour and walnuts. This can cause the cake to not rise.
For some extra flavour, add a pinch of cinnamon to the coffee loaf cake mixture.
You could make this in to a sandwich cake by slicing it in half and putting some buttercream in between the slices and then more on top.