The idea here is pretty simple. You melt pork fat without browning it, then strain it to remove the bits of meat, called cracklins. Many people melt lard on the stove, but the cracklins tend to sizzle and spit, causing nasty burns. The slow oven method is safer and easier. Cracklins are delicious in a taco or a salad. Ask your butcher for pork fat for rendering lard; it should be nearly meatless.
Preheat oven to 200° F. Cut 5 lb. (or more) pork fat into one-inch cubes. Cut away any large pieces of meat and reserve for another use. Spread the fat cubes in a roaster pan and place in the oven for 2 to 3 hours or until completely melted. Remove the pan from the oven, and being careful not to splash yourself, pour the melted fat through a colander lined with cheesecloth. Put the fat into clean jars and allow to cool, then store in the freezer until ready for use. Lard will keep for several months frozen.