Brown butter in a pan over medium heat, careful not to burn the
butter. Cool for 30 minutes.
Stir the cooled brown butter in a bowl with brown sugar and salt
until well blended. Add the eggs one at a time, and end by stirring
the flour and baking soda into the mixture until the flour is
incorporated. Stir in the chocolate, toffee and hazelnuts until evenly
distributed in the dough.
Form dough into a log, wrap in parchment paper and place in fridge
for at least 3 hours or until firm.
Preheat oven to 350 F.
Line a baking sheet with parchment paper.
Cut dough into 1/2 inch slices, place on baking sheet, and bake for
11-13 minutes, or until edges are golden. Let cool at least 20
minutes before eating, as toffee will have liquefied and will burn
your mouth. Once cool, enjoy!