Best way to sharpen a brush hog blades?

I recently heard of a new way to sharpen the blades on my brush hog, they said to take a cutting torch and just barely shave it off were its as sharp as a razor, I always just used a grinder, so whats best and whyBest way to sharpen a brush hog blades?
In the field that will work, but wouldn't recommend routinely doing it, you may also take the temper out of the blade with the torchBest way to sharpen a brush hog blades?
grinder