Preheat the oven to 200°F.
Place pork fat into a colander or mesh strainer.
Place colander or mesh strainer over a large stockpot, preferably a 10-quart tall stockpot. (You need a tall stockpot because it is important that the colander or mesh strainer does not touch the rendered lard as it drips into the stockpot from the colander or mesh strainer.)
Place the stockpot with the colander or mesh strainer filled with the pork fat into the oven.
Allow the pork fat to begin to render for one hour.
At one hour, open the oven door and check on the pork fat. Using potholders, carefully lift the colander or mesh strainer while keeping it over the stockpot. You should see that the pork fat has begun rendering, and the lard should be dripping down into the stockpot. (See video.)
Using potholders, carefully lower the colander or mesh strainer back on top of the stockpot and close the oven door.
Raise the oven temperature to 225°F and allow the pork fat to continue to render for at least five hours.
After five hours, open the oven door and look at what remains in the colander or mesh strainer. These are pork cracklings. They are bits and pieces of meat and blood that do not render into lard. If they appear brown and crisp, you have successfully rendered all the lard from your pork fat.
Turn off the oven, and using potholders, carefully transfer the stockpot with the colander or mesh strainer to a heatproof surface.
Transfer the cracklings from the colander or mesh strainer to a paper-towel-lined plate and allow them to cool slightly. These are best enjoyed when freshly made as they will become soggy if refrigerated.
Next, using potholders, pick up the stockpot by its handles and pour the lard through a mesh strainer placed over a bowl. (You do not need to line the mesh strainer with a cheesecloth or flour sack towel.) This extra step ensures that you will remove any small bits of cracklings that may have leached into the lard.
Using a ladle, transfer the warm lard into clean pint-sized jars. Allow a minimum of one inch of headspace from the top of the jar to allow for expansion if you decide to freeze the lard.
Allow the warm lard to cool to room temperature, and then place a lid on each jar and store them in the refrigerator or freezer. The lard will stay fresh in the refrigerator for 1 year and 2 years in the freezer. (For storing lard at room temperature, see the Recipe Notes below.)