A hand tool with several curved steel wires or blades fixed to a handle, rocked through a bowl of flour and cold butter to cut the fat into small pieces coated with flour. This is the "cutting in" step of pastry, biscuits, scones and crumble topping: the fat stays in distinct cold lumps that melt in the oven and leave flaky layers, instead of being rubbed warm and greasy by the fingers. Also called a pastry blender.
A food processor pulsed briefly does the same job faster but easily goes too far; two knives or a fork are the slow alternative. The tool also mashes avocado, eggs for egg salad and cooked beans. Stop when the largest pieces of butter are the size of peas.