Preheat oven to 350 degrees. Grease a 9 x 13 baking pan with cooking spray and line with parchment paper, set aside.
Brownie Layer. In a bowl, whisk eggs until frothy. Stir in sugar, flour, walnuts, and salt. In a seperate bowl, whisk together melted butter and cocoa powder. Add to egg mixture and whisk well to combine. Pour into bottom of baking pan and set aside.
Blondie Layer. In a bowl, cream together the butter and brown sugar. Add eggs and vanilla and mix well. Stir in flour, salt, and nuts. Spoon small blobs of the blondies over the brownie layer in the pan. Spread with a knife being careful not to stir together the two layers.
Bake for 25-30 minutes until the bars begin to pull away from the sides of the pan. Cool on a wire rack.
Icing Layer. In a saucepan over medium heat, bring the butter, sugar, and milk to a low boil then reduce to simmer. Simmer for 2 minutes. Remove from heat and cool slighly. Stir in the powdered sugar. Spread over cooled brownies.
Drizzle. In a small bowl, microwave the chocolate chips and coconut oil, stopping to stir every 15 seconds until just melted. Drizzle over the icing layer. Cool completley before cutting.
Notes
These bars are perfect for every occasion. Guests will be amazed by the layers. Make ahead and store in an airtight container in the refrigerator for up to a week.