- 1/2 cup 1 stick unsalted butter
- 1 cup dark brown sugar (packed)
- 1 large egg
- 1 tablespoon vanilla extract
- 1 cup all-purpose flour
- 1/4 teaspoon kosher salt
- 1 cup butterscotch chips
- Preheat oven to 350F. Line an 8-by-8-inch pan with aluminum foil or parchment paper and spray with cooking spray; set aside.
- Place butter in a medium sauce pan and heat over medium-low to medium heat. Butter will melt, then begin to bubble and foam. Brown specks will begin to form in the bottom of the pan, with a white foam will appear on top of the melted butter. Stir the butter very frequently to prevent burning. It should smell very nutty and the butter in the bottom of the pan should have brown flecks in it. This process should take 2-4 minutes. Butter can go from being browned and nutty-smelling to burnt and inedible in less than one minute. Watch for the brown specks and once you see them, remove the pan from the burner, continuing to whisk for another 30 seconds. Transfer butter into large mixing bowl and allow it to cool for a few minutes.
- Add the brown sugar to the browned butter and whisk to combine. Add the egg, vanilla, and whisk to combine. Add the flour, salt, and stir until just combined, taking care not to over-mix. Fold in the butterscotch chips. Pour batter into prepared pan, smoothing it lightly with a spatula or offset knife.
- Bake for 15 to 20 minutes, or until the bars are set. The edges will be slightly pulling away from sides of pan. Allow bars to cool for at least 2 hours before slicing and serving into 16 squares. I like to refrigerate them before cutting to make them easier to cut. Bars can be stored in an airtight container at room temperature or in the refrigerator for up to 1 week, or in the freezer for up to 3 months.