Preheat the oven to 350°F (175°C). Line a 9x9 inch baking pan with parchment paper, leaving some overhang for easy removal.

In a mixing bowl, combine the melted butter and sugar, whisking until smooth. Add the eggs and vanilla extract, mixing until well combined.

In a separate bowl, whisk together the cocoa powder, flour, salt, and instant coffee granules. Gradually add the dry ingredients to the wet mixture, stirring until just combined.

Pour the brownie batter into the prepared baking pan, spreading it evenly. If desired, sprinkle chocolate chips and walnuts on top.

Bake in the preheated oven for 25 minutes, or until a toothpick inserted into the center comes out with a few moist crumbs.

Remove the brownies from the oven and let them cool in the pan for about 10 minutes. Use the parchment overhang to lift them out and cool completely on a wire rack before cutting into squares.