Freeze the fat for a few minutes so it's easier to cut through. Get the crockpot (or dutch oven) heating up on low. Then, pour yourself a glass of two-buck-Chuck, because we all know sharp knives and wine work well together.
Cut the fat into 1/2″ chunks. Alternately, you could grind the fat in your food processor. This will help it to melt (or render) more quickly. I was in no hurry this time, so I simply cut it into chunks and threw it in the crockpot.
Cover the tallow and allow it to heat up to a simmer. Stir whenever you pass by to ensure the fat doesn't burn. Basically, it'll melt.
Once the bits of meat and fat left in there have become “crispy” (like the texture of well-cooked bacon), the tallow has finished rendering. Use a slotted spoon to remove the large chunks left (I gave my “cracklings” to Toby, our dog!).
Pour the rest of the hot fat (BE CAREFUL!!!!) through a small, mesh strainer or throw a colander lined with cheese-cloth.
Store in mason jars and allow the tallow to cool to room temperature. Store in the fridge and spoon it out, as needed.