Cutting cold butter into flour - which mixer attachment should I use?
Since you ask about other tools, I recommend avoiding the mixer altogether and instead grate frozen butter into the flour. If you have a food processor you can use the coarsest grating blade--chilling the bowl and grater first will help keep the butter cold will help--but it goes quickly by hand with a coarse grater.

The key is to get the butter distributed quickly and keep the butter and dough cool while working the dough as little as possible. If you do use the mixer, chilling the bowl and paddle helps. 

And, regardless of method using ice water and very cold liquids helps.