1 stick butter
1 cup packed dark brown sugar
1/2 tsp salt
1 tsp vanilla extract (or the seeds of one vanilla bean)
1 cup all purpose flour
1/2 cup heath bar crumbles
1/2 cup roughly chopped walnuts
Preheat your oven to 350 and butter an 8-inch square pan.
Brown your butter by melting it over medium heat on the stove until it becomes a golden caramel color (see here for more tips). Be careful not to burn the butter---you only want to brown it. This will take several minutes and it's easiest to keep swirling the pan with your hand while it browns.
Pour the browned butter into the bowl of a kitchen aid and add the brown sugar. Beat for about four minutes, until creamy. Add the egg and beat again. Then, add the flour, salt and vanilla extract (or seeds). Beat until combined.
Fold in the heath bar bits and chopped walnuts. Spread out mixture in your buttered pan and bake for 25 minutes, or until edges begin to pull away from the sides of the pan.Let cool before slicing into squares.