Sourdough Discard: In order to avoid a stronger sourdough flavor, use sourdough discard that is fresh or no more than a day or two old. I try to use active starter, as it results in softer, fluffier blondies.
Mix-Ins: I like a combination of butterscotch chips and cashews in these blondies, but you can use any mix-ins that you want. Toffee bits, milk chocolate, white chocolate - anything you'd like.