The toothpick test we usually do for cakes does not work in the case of brownies and blondies. The centre is generally gooey and fudgy, so even if we insert the toothpick, you'll end up with some sticky batter. If you continue baking because of that, you will overbake them, and they will have burnt bottom. For the doneness, you have to look for cooked to and some light browning.