Instructions

1. 1
   Line a baking sheet with baking parchment.
2. 2
   Melt the butter, sugar and salt in a saucepan over medium heat. Add water if necessary to keep fat from separating. Continue to cook until the temperature is 150°C (302°F) and when dropped in water it forms brittle threads.
3. 3
   Pour the toffee onto the prepared baking pan. Freeze until ready to use, about 30 minutes.
4. 4
   Meanwhile, line another baking sheet with parchment.
5. 5
   Melt the butter in a saucepan and cook until it turns dark brown. Remove from the heat.
6. 6
   Add an ice cube to the butter and let it melt. Repeat with remaining ice cubes.
7. 7
   Combine the sugars, espresso powder, salt, and baking soda in a large bowl.
8. 8
   Pour the brown butter into the sugar mixture and beat until combined.
9. 9
   Beat in the eggs and vanilla.
10. 10
    Fold in the flour until combined.
11. 11
    Remove the toffee from the freezer and break into chunks. Put into a zippable bag and break into bits using a rolling pin.
12. 12
    Add the toffee and chocolate to the dough and fold in.
13. 13
    Scoop the dough onto the baking sheet and let it chill for 48 hours for flavors to develop.
14. 14
    When ready to bake, preheat the oven to 163°C (325°F). Line 2 baking sheets with baking parchment.
15. 15
    Arrange the cookies on the baking sheets, leaving at least 2 inches (5 cm) of space between each other.
16. 16
    Bake for 18–20 minutes until golden brown.
17. 17
    Take the cookies out of the oven and sprinkle with a little sea salt before leaving them to cool.