This method requires you to first obtain the
trophy, gained after escaping Dimitrescu Castle. If you haven't got there yet, stop reading this guide to avoid possible spoilers.
Once you've defeated Lady Dimitrescu, you'll come across Duke in the village, he'll then ask you to retrieve another piece of the winged key. Upon return, you'll unlock a new area: Potter's Field. Save your game in the typewriter next to the shop and follow the path up the hill until you see a crow flying above you. There'll be a large tree in front of you, turn it left and you'll see three crows devouring a corpse, equip your shotgun and approach them. Shoot as soon as they start flying. Restart the most recent checkpoint and repeat until you get five.
Here is a video showing the method: