1. Preheat oven to 180degrees C.
2. Using an electric mixer, beat 440g castor sugar and 4 eggs in a large bowl until thick.
3. Fold in 225g plain flour (sifted) and 1/4 tsp salt.
4. In a separate bowl, combine 150g butter (melted) and 2½ tbsp cocoa powder, stir until smooth and fold into egg mixture with 1 tbsp Tia Maria.
5. Fold in 90g walnuts (toasted and chopped) and pour mixture into a 25-centimetre square cake tin greased and lined with baking paper.
6. Bake for 45-55 minutes or until cooked when tested with a skewer.
7. Cool cake in tin and then cut into squares.
8. Serve with vanilla ice-cream.