You can do rub the oil over the cauliflower with a brush, but it’s easier with your fingers – and much more fun. Didn’t you like finger-painting in kindergarden? As long as you wash your hands afterwards, you’ll enjoy “manhandling” your food. Next thing you know, you’ll be kneading bread!
In deference to Michael, I left the direction for spreading the butter as “smear”. But to me, it’s “schmear” as they used to say in the NY delis.