Hi Villimar and welcome to GoY. From your question I think you mean a Tree Peony the RHS has lots of info on, just copy and paste the link below:

https://www.rhs.org.uk/advice/profile?pid=711

Basically though it takes several year for a Tree Peony to get to flowering size, as you cutting it back at all as you may be removing the flower buds if done at the wrong time.

welcome to GoY from me too.
I find they take a while to settle once planted out. they have to re-establish roots. so the flower you had had been 'made' the previous year. you planted it , it flowered and then last year it was settling in. they need very little pruning in my experience.
the link suggested will be very good.

thank you