- Preheat oven to 350°F. 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 heat. Butter will melt, then begin to bubble and foam. Brown specks will begin to form in the bottom of the pan and 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. Remove the butter as soon as you see brown specks, remove the pan from the heat and continue to whisk for 30 seconds. Butter can go from being browned and nutty-smelling to burnt and inedible in less than one minute. Transfer butter into large mixing bowl and allow to cool for a few minutes.
- Whisk the dark brown sugar into the browned butter. Add the egg, vanilla, and whisk to combine. Add the flour, salt, and stir until just combined, taking care not to over-mix. Pour the batter into prepared pan and smooth it lightly with a spatula or offset knife.
- Prepare the maple pecan layer. Melt butter in a saucepan over medium heat. Once melted, whisk in the brown sugar and maple syrup until brown sugar is dissolved. Bring to a boil, stirring occasionally. Once it reaches a boil, cook for 1 minute and remove from heat. Add heavy cream and stir. Stir in the chopped pecans. Pour the pecan mixture evenly over the blondie batter and smooth the top with an offset spatula.
- Bake for 30-35 minutes or until the bars are set. Allow bars to cool completely 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.