Preheat your oven to 180°C.
Line the tray with baking paper.
Grease it lightly with butter.
This prevents sticking later on.
Beat butter and sugar until fluffy.
This takes about 3 minutes.
Add eggs one at a time.
Mix well after each egg addition.
Dissolve coffee granules in hot water.
Let it cool for a minute.
Fold in the flour gently now.
Add the coffee mixture and mix.
Stir in chopped walnuts carefully.
Pour mixture into prepared tray evenly.
Smooth the top with a spatula.
Bake for 25-30 minutes until golden.
Test with a skewer—it should come clean.
Beat butter until it's really soft.
Add icing sugar gradually while mixing.
Dissolve coffee in hot water first.
Add coffee to the butter mixture.
Beat until light and fluffy texture.
Let the cake cool completely first.
Spread icing evenly over the top.
Arrange walnut halves on top nicely.
Cut into squares and enjoy immediately!