Cook the butter over low heat until browned. Pour into a clean bowl Add brown sugar and vanilla and mix until fully combined.
Make Brown Butter
Mix in the egg, make sure there is no trace of egg yolk left behind.
Add the Egg
Add flour, baking soda and salt, and gently mix until no flour streaks remain.
Add the Dry Ingredients
Fold in chocolate chunks and pretzels.
Pour into a prepared pan. Bake for 23-28 minutes.
Let cool on a wire rack for at least an hour before slicing.
Cool and Slice