Bake for about 20 to 22 minutes (or until done based on add-ins used). Top should be set and edges slightly firm. A toothpick inserted in the centre (if you can find a bare patch to test) should come out clean, or with a few moist crumbs, but no batter. Allow bars to cool in pan for at least 30 minutes before slicing and serving. Bars will keep airtight at room temperature for up to 1 week, or in the freezer for up to 6 months.