Get you a Whirley-Pop. You can put the butter in with the kernels go.
You can also get packs that include oil, kernels, salt, and butter powder that come out like theater popcorn and taste great (included some in the link above). I add some cheddar powder to that for cheesy popcorn when we have people over to watch movies and it’s a huge hit.
Edit: important note, add the cheddar powder AFTER popping, because it will burn if you put it in before popping and it will smell awful. Don’t make my mistake!