In a bowl, sift together the flour, cocoa powder, baking powder, and coffee powder. In a saucepan, melt the butter over low heat without letting it separate. Add the sugar and mix well.

Add the eggs and vanilla to the butter mixture and mix.

Pour this mixture into the dry ingredients and stir well to form a batter. Add the raisins and chopped walnuts and mix.

Preheat the oven to 350°F (178°C). Grease a 7 x 9 1/2 inch (17 x 24 cm) baking pan with oil or butter, or line it with parchment paper. Spread the batter evenly in the pan and decorate the top with extra walnuts. Bake for about 25 minutes.

Once baked, let cool completely. Cut into squares of your preferred size. I cut mine into 3 rows lengthwise and 5 rows widthwise, for a total of 15 pieces.