Preheat your oven to 250°F.
Cut the beef fat into large chunks. There's no specific size required, just ensure the pieces are manageable and not in one large block.
Place the chunks of beef fat into an 8x8 baking dish, spreading them evenly.
Bake in the preheated oven for 3 hours, allowing the fat to slowly render.
Remove the dish from the oven carefully, as the contents will be hot.
Pour the liquid fat from the baking dish through a fine mesh strainer into a heat-safe, pourable measuring cup or bowl. This will help remove any solid particles.
Immediately pour the strained liquid into mason jars or similar airtight containers, securing the lids while the fat is still warm.
Let the jars cool to room temperature. Tighten the lids once more and place the jars in the refrigerator for 48 hours or until the tallow is fully set.