I'm a seasoned baker - I've been baking for the best part of 4 decades and have few disasters. The few I've had come from following a new recipe and not trusting my instincts when something seems a bit off, or from using ingredients which turned out not to be up to the job.
Anyhow, I attempted to show DS1 how easy shortbread was to make, this afternoon. He's sample a bit of shop bought stuff lately, some much nicer than others (we got given a hamper with some made with marge - ugh! He noticed the difference when we bought a tin of good quality buttery stuff from Sainsburys at Christmas)
I used a simple 3-2-1 recipe. The same as I was taught to make by my parents (dad used to cook for a living) and have made many times. Rubbed in method. Only it completely refused to bind. I just had a bowlful of crumbs. Ended up binding them with egg yolk just to rescue something and then pressing into a tin like a cheesecake base. Now have palatable biscuits, but shortbread they're not.
Al I can think of is that my kitchen has been a little on the cold side, today and for the past few days. Have had to put butter through the microwave to get it to a spreadable consistency. Stands to reason that my flour and sugar probably set the softened butter, again.