How to rub butter into flour for a crumb topping
Start with small pieces of cold butter and stop when the crumbs have the size your recipe needs.
Use a bowl wide enough to get both hands into the mixture. Combine the flour with any sugar or spices specified for the topping, then add cold butter cut into even pieces. Toss the pieces in the flour so they stay separate while you work.
Pick up a few pieces at a time and press them lightly between your fingertips and thumbs. Rub the butter into the surrounding flour and let the crumbs fall back into the bowl. Turn the bowl as you go. Lifting from the bottom brings up flour that the first few handfuls can miss.
For a fine, sandy finish, keep rubbing the largest pieces down. For a crumble with a few knobbly clusters, squeeze a handful of the mixture once, then break it into bite-size pieces. If your hands start leaving greasy marks on the butter, cool the bowl before continuing. Scatter the finished crumbs evenly over the fruit or cake.
