Preheat oven to 325°F. Spray a 9x13-inch pan with cooking spray, line with parchment paper and leave an overhang for easy removal. Melt butter in microwave and set aside to cool to room temperature. Hot butter will melt the sugars and cause greasy bars.
Whisk melted butter and sugars until smooth. Add egg, yolk, vanilla, and syrup. Whisk until smooth and emulsified.
Use a wooden spoon to stir in baking soda, salt, and flour until just combined. Fold in chocolate chips. If needed, switch to a hand mixer, but don’t overmix. Press dough evenly into pan. If desired, press a few more chocolate chips into the top.
Bake for 23–28 minutes until top isn’t glossy and edges are lightly golden. Be careful not to overbake. Optionally top with sea salt right out of the oven. Fully cool in pan, lift out, cut, and serve.
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Notes
Note 1: You can discard egg white or save and add it to breakfast the next morning. I love this Egg Skillet and this Egg Wrap.Note 2: Maple syrup is the secret ingredient in these bars. In a pinch, you can leave it out, but the bars do lack a bit of tenderness and a certain level of sweetness. I use pure maple syrup, not to be confused with pancake syrup.Storage: Store bars in an airtight container in the fridge for up to 1 week. Wrap bars individually and freeze for up to 3 months. Thaw at room temperature before serving.