Get A Mooshroom Cow And Tie It To A Fence Or Trap It In Some Area Like How Shown In The Picture

Step 1: Chat

go to the chat and type /summon lightning_bolt whilst standing next to the mooshroom cow

Step 2: Done!

Now You've Got Your Brown Mooshroom Cow But 1 Last thing,

1. you get get mushroom stew by right clicking it with a bowl

2. you can get suspicious stew by right clicking it with a flower then a bowl

And You're Done!