Whisk the eggs and milk together in a large bowl.  Add the sifted flour and salt, and mix together thoroughly until there are no lumps.  (if there are lumps, pass the batter through a fine mesh sieve)  Cover the bowl with a towel, and let sit for 20 mins - 1 hour until ready to cook it.

When you are ready to cook the pudding, after you've taken the roast out of the oven, increase the oven temperature to 400 F (200 C).

Place the roast drippings in the bottom of a roasting dish, and swirl it around to completely coat the bottom of the pan.  Put the dish in the oven and let it heat until the fat begins to smoke.

Add 2 tablespoon cold water to the batter, whisk it together quickly, then pour it into the dish and put back in the oven.

Allow to cook until puffed up and golden brown, about 20 minutes.