Preheat oven to 350°F. Line a 9-by-13-inch baking pan with parchment paper or foil, allowing it to slightly overhang opposite edges. Coat with cooking spray.
Melt butter in a large saucepan over medium heat. Cook, swirling often, until fragrant and starting to brown, 4 to 5 minutes. Remove from the heat. Whisk in brown sugar; let cool for 15 minutes.
Meanwhile, whisk flour, baking powder and salt in a medium bowl.
Whisk eggs and vanilla into the cooled butter mixture until well combined. Add the flour mixture in two additions, gently folding until just combined. Reserve 2 tablespoons each pecans, chocolate chips and coconut; fold the remaining pecans, chocolate chips and coconut into the batter. Evenly spread the batter into the prepared pan. Sprinkle the reserved pecans, chocolate chips and coconut on top.
Bake the blondies until light brown around the edges, 18 to 22 minutes. They will appear slightly underbaked in the center; but will firm up as they cool. Let cool completely in the pan on a wire rack, about 2 hours. To cut, grab the overhanging parchment or foil and transfer the whole batch to a cutting board, then cut into 24 bars.
Notes
Make Ahead Tip: Cover and store airtight for up to 3 days; freeze for up to 3 months.Try white whole-wheat flour in place of all-purpose flour in baked goods. It’s made from hard white wheat berries, which makes it lighter in color and flavor than regular whole-wheat flour, but with the same nutritional properties. Look for it near other whole-grain flours. For the best flavor, store it airtight in the freezer.For the best flavor, toast nuts before using in a recipe. To toast sliced (or chopped) nuts, place in a small dry skillet and cook over medium-low heat, stirring constantly, until fragrant, 2 to 4 minutes.To Cut Perfect Bars: Grab the overhanging parchment or foil and transfer the whole batch to a cutting board, then cut into bars.