UPGRADES:
NUTMEG OR CINNAMON BLONDIES: Just before serving, grate a little nutmeg or cinnamon stick over the bars.
PEANUT BUTTER BLONDIES: Reduce the amount of brown sugar to ⅔ cup. Add ½ cup (3 oz) well-stirred natural peanut butter (chunky or smooth) with the brown sugar. Substitute ½ cup (2 oz) roasted salted peanuts for the walnuts.
PEANUT BUTTER HAZELNUT BLONDIES: Reduce the amount of brown sugar to ⅔ cup. Add ⅓ cup (3 oz) well-stirred peanut butter (chunky or smooth) with the brown sugar. Substitute toasted skinned hazelnuts for the walnuts. Before baking, sprinkle the top very lightly with tiny pinches of flaky sea salt.