Ok. You know how you can do flat ground 3s on the grounds. And those miniscule movements you do go keep your spinning going. You have to translate that to the nose part of your skis. I grab my noses with my hands and then recreate those movements(definitely more exaggerated then flat base). And you can get it done. A slight hill with a even fall line helps. I've got a full 1080 done before.
Now to be fair. I'm a shitty park skier. Full admit. But I have always loved buttering around.
Also. Start the first rotation kind of like a cork threw drop the shoulder you are turning into. Suck the legs up a tad to the perfect butter position! Think about making your balance point on the 10 inches of your nose
To me it has always been about shifting my body weight and how the ski contacts. When you butter 180 turn your head slowly and keep rotating, shift the weight over slightly to the opposite shoulder and balance the last 180 degrees of the butter