Place the suet in a food processor and grind well.
Place the ground suet and ⅓ of the salt in a stockpot and add enough water to completely cover the suet. Put it in the oven and turn it to 200 degrees.
Stir the mixture every 45 minutes until it has completely melted and pieces of gristle are floating on top. The time this takes will vary based on how finely you were able to grind or cut the tallow.
Strain the mixture through a fine mesh strainer and place it in the fridge until the tallow hardens on top of the water.
Wash the stockpot to use again.
Remove the hardened tallow and scrape the brown residue off the bottom of the disk. The water left in the bowl will be extremely dirty.
Place the tallow back in the clean stockpot along with half of the remaining salt and cover with fresh water. Place back in the oven at 200 degrees for about 2 hours or until the tallow has melted and gently simmered for about an hour.
Strain the mixture through a fine mesh strainer, this time with a cheesecloth spread over it, and place in the fridge until the tallow hardens.
Wash the stockpot to use again.
Remove the hardened tallow and scrape any brown residue off the bottom. There should be less than the previous time and the water left at the bottom of the bowl should look cleaner too.
Place the tallow back in the clean stockpot along with the rest of the salt and cover with water. Place back in the oven at 200 degrees for about 2 hours or until the tallow has melted and gently simmered for about an hour.
Strain the mixture, this time using a doubled cheesecloth over a mesh strainer and let sit at room temperature for an hour before placing in the fridge to finish hardening.
Once the tallow is hard, remove it from the bowl. Use a knife to scrape any discolorations off of it (there shouldn't be much left).
Use paper towels to dry it off as much as possible, and let it sit at room temperature to dry completely before storing.