Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
Beat butter, brown sugar, and granulated sugar until creamy.
Mix in the egg and vanilla extract.
In another bowl, whisk together flour, baking powder, salt, and instant coffee.
Gradually add dry ingredients to the wet mixture, stirring until fully combined.
Fold in ½ cup chopped walnuts.
Scoop dough into small balls and place them 2 inches apart on the baking sheet.
Gently press each ball and sprinkle with ¼ cup coarsely chopped walnuts.
Bake for 10-12 minutes until edges are golden.
Let cool slightly before devouring.