Brew an Awkward Potion by placing a Water Bottle in a Brewing Stand with Nether Wart
Add Magma Cream to the Awkward Potion in the Brewing Stand
Collect the resulting Fire Resistance Potion
Optional: Add Redstone Dust to extend the duration
Optional: Add Gunpowder to make it throwable as a Splash Potion
Optional: Add Dragon’s Breath to make it a Lingering Potion