Welcome to the Cake Decorators Q&A
Hi I make shortbread biscuits all the time
and my batch this week was crumbling at the edges
any idea why
it is very hot here in the 30s
I've never heard of weather heat being a factor in making cookies crumbly. However, that's only because it has never happened to me. I do know some climatic conditions can affect baking, such as high altitude or humidity which tend to make baking a bit wetter rather than dry. In those circumstances, it is a scientific reason which requires addressing.
I suppose if it's very hot by you, it is possible that you may be experiencing some moisture loss in your flour. Try placing your flour in the freezer for half an hour and see whether that makes a difference.
Also is it possible that your oven could be running a touch hotter than it should be? Sometimes ovens will step out of kilter and run slightly hotter in the cavity and not as the outside temperature gauge reads. If you have an oven thermometer, place it in the cavity on the middle shelf a little to the back and take a reading. If the outer dial reads higher than the inside, adjust the dial to read the same as the inner. Certainly, if the oven is running hotter, it will be over baking your shortbread.
If this is not the case, it may be that you have used a different butter/fat with less water content. Some butter contains a little less water which could make a difference to the outcome of your bake.
I feel oven temperature and moisture are the most likely reasons. Over kneading the dough can make it tough, but I don't think this is the case as you are used to making good shortbread at other times.
I hope these suggestions help. I'm so sorry I can't give a more definitive answer. 🙂