Preheat the oven to 175°C (350°F) and grease the loaf pan.

Dissolve 2 tablespoons of instant coffee granules in 4 tablespoons of boiling water.

Cream together the 225 g unsalted butter and 225 g brown sugar until light and fluffy.

Incorporate the 4 large eggs one at a time, mixing thoroughly.

Blend in the cooled coffee mixture until just combined.

Sift together 225 g all-purpose flour, 1 teaspoon baking powder, and 1 teaspoon salt.

Gradually fold dry ingredients into the wet mixture until fully incorporated.

Gently fold in 100 g chopped walnuts until evenly distributed.

Pour the batter into the prepared loaf pan, smoothing the top.

Bake for 45-50 minutes, or until a toothpick comes out clean.

Cool in the pan for about 10 minutes before transferring to a wire rack.

Allow to cool completely before slicing.