Lemon shortbread cookies should be neither totally crunchy or super soft. Rather they should be tender and crumble a bit in your mouth when you bit into them. Classic shortbread cookies are both buttery and tender, and "short". This is due to the high ratio of butter in the dough and the relative lack of extra liquids compared to the dry ingredients. The lack of gluten development is the reason for the perfect texture of these buttery cookies.