It could simply be a corruption, perhaps of 'a bully fine pie'?

It is rather old fashioned but a bully meal, feast, 'table'or a stew - and so presumably a pie, would be a 'slap up' or 'first rate' do or dish, feeding fit for men, ebullient in the exuberant sense, overflowing and abundant.

No soggy pastry over mostly air with a thin sad layer of something grey and gristly.

Desperate Dan's cow pie would be a bully fine pie.

Anne