In a large mixing bowl, cream together unsalted butter and granulated sugar until light and fluffy, about 3-5 minutes.

Add in instant espresso powder and salt, mixing until well combined; the dough should be smooth.

Gradually incorporate all-purpose flour into the butter mixture on low speed until just combined.

Gently fold in chocolate-covered toffee chunks into the dough.

Divide the dough into two equal portions and shape into logs; wrap in parchment paper and refrigerate for at least 2 hours.

Preheat oven to 350°F (175°C). Slice chilled logs into 1/4-inch thick rounds and arrange on a parchment-lined baking sheet.

Bake for 18-20 minutes, or until edges are lightly golden.

Let cookies cool on the baking sheet for about 5 minutes before transferring to a wire rack.