Start off with the cold fat. It is much easier to handle and cut than when it gets warm. Cut up the pig fat into small cubes trimming out any bits of blood, gristle, or meat. If you order your meat in bulk and get a half or whole pig, the processor may even grind up the fat for you making it ready to render without needing to cut it up. Having the pig fat in smaller chunks will help it melt and render more quickly.
Add fat chunks to the food processor and process until it is the consistency of ground beef or ground pork. If you don't have a food processor, that is okay. Chop the fat into smaller pieces to help it render more quickly.
Place fat in a crockpot for 5-6 hours on the "low" setting. If your crockpot tends to run hot, turn it to the "warm" setting as needed. The alternative to the crockpot is the stove top in a large stock pot. Turn it on a low heat. This method is a little quicker, but it is important to keep an eye on it and stir occasionally to make sure it is not burning. Whichever you choose, MAKE SURE TO USE A VERY LOW HEAT. Too high of heat risks burning the lard giving everything you make with it an unpleasant taste and smell.
You will know it is done when there is a clear liquid at the bottom of your pot and little bits of gristle floating on top. Pour through a cheesecloth, straining out the gristle and meat.
Pour liquid lard into wide mouth quart jar. Since the lard is smooth and sticky, especially at room temperature, a jar works well for storage. However, I do recommend wide mouth jars as they are easier to dig to the bottom as it runs out.