Preheat oven to 350 degrees Fahrenheit (180 degrees Celsius).

Beat eggs and sugar for five minutes until light and lemony. Add the rest of the ingredients, aside from the nuts, slowly, and mix until incorporated.

Fold in the nuts by hand, and pour into a 9×13-inch (20×30-cm) baking pan lined with Gefen Parchment Paper.

Bake for 35 minutes or until set. Do not overbake. Cool slightly, then cut into squares.

Mix together the cocoa powder, coffee granules, and boiling water until smooth. Cool slightly.

Add confectioners’ sugar and oil, and whisk together until a creamy, velvety texture is achieved. If necessary, add a bit more confectioners’ sugar to reach desired consistency.

Pour over cut brownies, tilting the pan to cover the entire surface. It’s best not to smear too much so it remains smooth and shiny. Sprinkle with chopped filberts, if desired. Let set before serving or freezing.