Preheat the oven to 350 degrees and set a rack in the middle of the oven
Line a baking tray with parchment paper and set aside.
In a bowl, whisk flour, baking soda, and salt together.
In a separate bowl, whisk the espresso powder and water until powder is dissolved. Next, whisk in sugar and melted butter until combined. Whisk in egg and vanilla extract and mix until smooth.
Using a spatula fold the dry ingredients into the wet ingredients and mix until a dough forms. Next, fold in the toffee bits.
Roll dough into balls about the diameter of a quarter and place on the prepared baking tray at least 2 inches apart.
Bake until edges are set but centers are still soft, around 13 minutes. Rotate pan 180 degrees halfway through
Let cookies cool on tray and serve warm. Store leftovers in an airtight container at room temperature for up to 3 days.