Preheat oven to 325 degrees. Butter or spray a 9x13-inch baking pan. Line bottom of pan with parchment paper; butter and flour parchment paper (or spray with baking spray).
In a skillet (preferably with a white bottom) over medium heat, cook the butter, stirring frequently until it bubbles. Increase stirring to continuously until the butter turns golden brown. Remove from heat and pour into a heat-safe bowl and let cool.
1 1/4 cups unsalted butter
In a medium bowl, whisk together flour, baking powder, and salt. Add pecans and toffee bits to the dry ingredients and toss to coat.
Attach bowl to mixer; add eggs. Using the paddle attachment, beat on medium-high speed until light and fluffy, about 3 minutes.
3 large eggs
Add vanilla, and beat to combine. Reduce speed to low and add flour mixture. Mix until thoroughly combined, and spread into prepared pan.
2 1/2 teaspoons pure vanilla extract
Bake 35 to 40 minutes or until a toothpick inserted in the center comes out clean (do not overbake). Transfer to a wire rack to cool completely before turning out of the pan onto a cutting board. Peel off parchment paper; cut blondies into 2-inch squares.
It's best to use a kitchen scale when measuring for the best possible outcome in your baked goods. If you do not own a scale, I would recommend using the scoop and sweep method when it comes to flour. Scoop the flour into a measuring cup using a spoon and level it off gently with the back end of a butter knife. Never pack your flour or tap the cup on the counter to condense. Too much flour will result in dry, crumbly baked goods.
You can typically find chocolate covered toffee bits in the baking aisle next to the chocolate chips. If you can't seem to find them, you can easily chop up some Heath candy bars for the same result or substitute them with regular toffee bits.