Adjust oven rack to middle position and preheat oven to 350°F. Spray an 8x8-inch square baking pan with nonstick cooking spray.
In a medium mixing bowl, whisk the flour, salts, and baking soda together. Set aside.
1 cup all-purpose flour, 1 teaspoon kosher salt, ¼ teaspoon coarse sea salt, ¼ teaspoon baking soda
In a heavy, large saucepan set over low heat, melt butter. Remove from heat and add brown sugars.
½ cup unsalted butter, ½ cup dark brown sugar, ¾ cup light brown sugar
Cool mixture for 2 minutes and add eggs and vanilla; whisk until smooth.
2 large eggs, 1 teaspoon pure vanilla extract
Use a rubber spatula to stir in the flour mixture and half of the chocolate and the peanut butter chips. Also, add half of the peanuts, if using.
½ cup milk chocolate chips, ½ cup peanut butter chips, ½ cup salted honey roasted peanuts
Spread batter evenly in the prepared pan and sprinkle with the remaining chips and peanuts.
Bake at 350°F for 25-35 minutes or until a toothpick inserted in the center comes out clean – the edges should just begin to pull away from the sides of the pan.
Transfer the Blondies to a cooling rack and leave in the pan to cool completely.