Source: based on Cook's Illustrated , but tweaking has occured
1 1/2 cups unbleached all-purpose flour (7 1/2 ounces)
1 teaspoon baking powder
1/2 teaspoon table salt
12 tablespoons unsalted butter (1 1/2 sticks), melted and cooled
1 1/2 cups packed light brown sugar
2 large eggs
1 1/2 teaspoons vanilla extract
1/2 cup semisweet chocolate chips
1/2 cup toffee chips
1 cup pecans, toasted and chopped coarse
1 1/2 cups sweetened coconut flakes, toasted
Adjust an oven rack to the middle position and heat the oven to 350 degrees. Line a 13 by 9-inch baking pan with two pieces of foil. (See note below.) Spray the foil-lined pan with nonstick cooking spray.
Whisk the flour, baking powder, and salt together in a medium bowl; set aside.
Whisk the melted butter and brown sugar together in a medium bowl until combined. Add the eggs and vanilla and mix well. Using a rubber spatula, fold the dry ingredients into the egg mixture until just combined. Do not overmix. Fold in the semisweet and white chocolate chips and the nuts and turn the batter into the prepared pan, smoothing the top with a rubber spatula.
Bake until the top is shiny and cracked and feels firm to the touch, 22 to 25 minutes. Place the pan on a rack and cool completely. Cut into 1 1/2 by 2-inch bars.
NOTE: Removing Bar Cookies from the Pan: Place two sheets of aluminum foil or parchment paper perpendicular to each other in the pan, pushing the foil or paper into the corner. After the bars have baked and cooled, use the foil or paper to transfer them to a cutting board, then slice into individual portions.
My notes: The original recipe calls for white chips. I'm not fond of white chocolate for the fake white chips, so I first tried butterscotch chips as a substitute. I wasn't happy with the fake flavor the butterscotch chips lended, so I tried toffee chips and was much happier. In the original recipe, coconut is optional, but I definitely think of coconut when I think of blondies - still, it can be left out if you don't care for coconut.