OK, that's rather like my recipe then :) I ask because I've been through EXACTLY that issue with the cold butter, and was visualising a well-mixed cake batter with a big yellow rectangle floating in it ;)

When I do it, I mix the butter and sugar together (electric hand mixer or vigorous wooden spoon action) til creamy, then add the egg, then throw everything else in.

Also I like walnuts in mine rather than choc chips :)