This is usually caused by the ratios being off. Shortbread is a very simple recipe, just flour, butter and sugar. Look for a recipe that gives you amounts by weight, rather than volume. read more
classic shortbread proportions are 3 flour, 2 butter, 1 sugar. I cream 3oz sugar with 6oz butter, then mix in 8oz plain flour and 1oz cornflour/ground rice. I find this way doesn't make it so crumbly, though my mum does the 'rub it in together until it clumps' method and her shortbread usually works too. read more