Place a rack in the center of your oven and preheat to 350 degrees. Grease an 8-inch square baking pan, then line with parchment paper, allowing the paper to overhang the edge on two sides. Grease and flour the pan, then tap out any excess flour. Set aside.
Melt butter, applesauce, and honey in a saucepan. Stir in the brown sugar, then transfer to a mixing bowl.
Stir in the egg and vanilla extract until smooth.
Add the white whole wheat flour, all-purpose flour, and salt, and mix until just combined. Let the batter cool 20 minutes, then stir in the chopped pecans.
Transfer the batter to the prepared pan, smoothing the top and spreading the batter as evenly as you can. If desired, sprinkle lightly with flaky salt.
Bake the pecan blondies until the edges are browned and the center is set, 24 to 28 minutes. Set the pan on a wire rack to cool completely, then use the parchment to lift blondies out of the pan. Cut into squares and serve.
Notes
TO STORE: Honey bars may be stored, at room temperature, in an airtight container for up to 3 days.
TO FREEZE: Wrap the bars individually in plastic wrap and store in the freezer for up to 3 months. Defrost overnight in the fridge or on the counter for a few hours before serving.
TO REHEAT: For a fresh-baked taste, warm leftover honey bars for a few seconds in the microwave until warm.