The traditional method for rendering tallow from an intact piece of suet that you can obtain from a pastured farmer.
Take an intact piece of suet and cut into medium to small pieces on a large cutting board. Remove the kidney and set aside.
Place the suet pieces in a large pan.
Place pan in an oven preheated to 175-200 °F/ 79-93 °C
Every hour or so, remove the pan and pour off the melted tallow. Sieve through a cheesecloth to remove any tissue.
Continue the process until all the fat has rendered. This will take a few hours. Tallow is quite yellow when it is liquid.
Pour strained tallow into glass mason jars after it has cooled. Screw on the lids and refrigerate. As it hardens in the fridge, tallow turns a whitish beige color. Tallow will keep for many months in the refrigerator and a year or more in the freezer.