Definition: working cold fat into flour with your fingertips until it looks like breadcrumbs — the base method for pastry, scones and cobbler toppings.
Rubbing-in is one of the first techniques worth getting comfortable with. You take cold, cubed butter and flour and rub them lightly between your fingertips, lifting your hands to let air in, until the mixture looks like fine breadcrumbs. Keeping everything cool matters: little flecks of unmelted butter are what give scones and cobbler toppings their flaky, tender bite once they hit the oven.
In practice: cold butter, a light touch, and stop at breadcrumbs — don’t work it into a paste.
Related:self-raising flour,crumb.