Optional pre-step: blanch the lard in boiling water before rendering. Chinese cooks believe this reduces the sour pork smell! Also, rendering lard produces a strong smell. Make sure to open your windows and shut bedroom doors!
Cut your partially thawed or chilled pork fat into equal sized, small pieces. (For easier cutting, put the fat in the freezer for 10-15 minutes to firm it up. Don't work with room temperature fat as it's slippery.) Alternatively, get your butcher to grind it or blitz it in your food processor.
Add the cut-up pork lard (and water and aromatics, if using) to a heavy-bottom pot which allows for even heating. Use a Dutch Oven if you have one. (A flimsy pot is also dangerous, as you can easily overturn it and the rendered lard is HOT.)
On low heat: melting pork fat needs to be a slow process. (Using high heat gives the lard a stronger porky taste.) Set the fire on 2 (mine's a Bosch induction with a maximum of 9.) Stir the fat to prevent sticking and burning.
When you see the fat melting/ oil oozing out, reduce to 1 (lowest heat possible.) Note that it is more difficult to tell when the oil is oozing out with wet vs dry rendering.
Stir every 30 minutes or when you hear sizzling. Don't let the fat stick to the bottom or sides of the pot, or your lard will taste porky!
The lard will eventually start bubbling so don't be alarmed. (The bubbles indicate that there is still moisture in the fat. You're always using low heat so you should never be boiling the lard.)
The fat will take 2-4 hours to completely render. Make sure that there are no more bubbles and the crackling (pork bits) have risen before switching off the fire.
Remove the golden brown scratchings. I recommend sieving using a strainer or cheesecloth. You can also crush the scratchings to get every bit of oil out.
Place the pork scratchings on a kitchen towel to absorb the excess oil. If not as crunchy as you like, pop them into a dry pan, air fryer or oven for a few minutes (350F/ 177C)
Filter the pork lard into a sterilised, heat resistant glass jar- this is particularly important if you've added aromatics to your lard. Allow it to completely cool before covering and refrigerating.
Keep it for up to 6-9 months in the fridge and do not use if rancid (smells bad) or moldy. (Some people say 12 months- I like to err on the side of caution! You can freeze if it you want it to last longer.)