Preheat oven to 350°F (175°C) and line a baking sheet with parchment paper.
Cream butter and brown sugar until fluffy.
Add instant coffee, egg, and vanilla, mixing well.
In a separate bowl, whisk flour, baking soda, and salt.
Gradually add dry ingredients to the wet mixture, stirring until combined.
Roll dough into 1-inch balls and place 2 inches apart on the baking sheet.
Bake for 9-10 minutes, or until edges are lightly golden.
Cool on the sheet for 5 minutes, then transfer to a wire rack.
Try not to eat them all at once.
Store in an airtight container—if they last that long.