You can easily grind for this in the secret level titled “Moo.”
Difficulty: Default Tier: VI(6)
Once you beat the game, lower the draw bridge, and enter the church, you will be tasked with finding the 9 runes, each scattered variously throughout every level. The link to help you out with the runes is posted in the spoiler at the bottom of this guide
Once you have done that, Head back to the church and the level will unlock.
All you have left to do is hack and slash at all the mooshroom. I went from level 40-42 by the end of the level. It is a good idea to have a melee weapon with a high DPS, like a claymore or hammer, and heavy armor with damage reduction and a chance to negate hits... They drop strength potions fairly often. My setup was heartstealer claymore with stalwart armor. I used a level 40 harvester artifact to insta kill crowds of mooshroom by herding them all together.
I suggest saving all arrows for the boss battle if you want to fight it. I have a fairly easy way of trapping the boss by running around one of the corners and dropping below him by one block to stay underneath his attack while he’s stuck from moving. I attached an image for that.
Good luck!
P.s. please note that I’m not trying to hijack the other solution or copy the comments. But you can’t view the comments made for that solution on the Xbox TA app.