Place butter in small saucepan and cook over medium heat until a golden brown color with a nutty smell. Set aside and allow to cool.
Add sugars to mixing bowl, pour in the cooled brown butter and mix until combined. Add in the egg and vanilla extract, mix on low speed until combined.
In medium size bowl combine the flour, baking soda, and salt. Whisk to combine. Slowly add the dry ingredients to the wet. Mix on low speed until dough is just combined. Fold in the toffee, chocolate chips and pretzel pieces.
Chill the dough for at least 30 minutes.
Preheat oven to 350°F.
Prepare baking sheet with baking spray or parchment paper. Spoon dough onto the cookie sheet using a cookie scoop or tablespoon.
Bake for approximately 8 minutes or until golden on edges.
Remove from the oven and let cookies cool on the pan for 5 minutes, then remove to cool on a wire rack.