In a mixing bowl, whisk or beat together the flour, salt, and eggs until relatively smooth. Gradually add the milk, whisking until the batter is smooth and lump-free.
Cover with plastic wrap and refrigerate for at least 2 hours and preferably overnight for maximum flavor. The longer the batter rests, the better the flavor will be.
Preheat the oven to 450 degrees F. Using a traditional Yorkshire pudding tin, place a teaspoon or two of beef tallow in each tin and place the tin in the oven for about 6 to 7 minutes until piping hot.
Pour the batter into each tin (the pan should be hot enough that the batter sizzles) between 1/2 to 3/4 full. If making two large Yorkshire puddings in two 8-inch cast iron pans, fill each pan slightly less than half full.
Bake the Yorkshire puddings for 11 to 13 minutes or until a deep golden brown. Serve immediately. Traditionally served with a roast, roasted potatoes, veggies, and brown gravy.