It was the ultimate "Big Mac" attack, but not the kind that sends you out to McDonald's at midnight in search of two hamburgers on a sesame seed bun with pickles and a mystery sauce.

And it took the Ellery Queen sleuthing talents of two physicians to find out why a Canadian woman almost died when she ate a Big Mac.

It also took the cooperation of the McDonald corporation, which had to reveal its "secret" sauce ingredients to the doctors so they could figure out what caused a 35-year-old woman, having difficulty breathing, to be rushed to a Montreal hospital. Her larynx was nearly swollen shut and she had the typical symptoms of an allergic reaction: itching, abdominal pain and hive-like swelling on her face.

The culprit: gum tragacanth, a common food additive, used as a thickener and stabilizer in a number of processed foods including salad dressing. While its ability to cause an allergic reaction has been known for years, it is considered safe by the Food and Drug Administration, and even consumer activists who worry about such things have never singled out gum tragacanth as harzadous.

Ruth Winter's comprehensive guide, "A Consumer's Dictionary of Food Additives" (Crown, $8.95), describes it as "one of the oldest known natural emulsifiers. Aside from occasional allergic reaction, it can be ingested in large amounts with little harm except for diarrhea, gas or constipation."

The ultimate "Big Mac" attack, not the kind McDonald's hopes will overtake people, came to light in the May 11 issue of the New England Journal of Medicine. Doctors from McGill University Teaching Hospital in Montreal wrote to the Journal to "alert other physicians to this hidden allergin . . . in view of the widespread consumption of Big Macs."

The doctors also explained that the woman who had the attack has a history of allergic reactions to various substances from pollen to aspirin.

The recipe that holds the unenviable distinction of having put a cookbook in the same category as a faulty automobile, subject to recall, has been around for years. Probably as long as the single ingredient in it - condensed milk.

Earlier this month Woman's Day Crockery Cruisine cookbook was recalled because a recipe, which instructed the cook to place on unopened can of condensed milk in a crock pot, ommitted the cooking medium - water. Without the water the crock pot could and did explode.

You don't need a pot to make Dulce de leche, just a can of unopened condensed milk and a pot filled with water.When the recall story was reported the Sisterhood of Congregation Har Shalom in Potomac, Md., sent in this recipe from its cook book, "Pot of Gold." DULCE DE LECHE ("Sweet from milk")

This is a caramel spread you won't believe until you taste it on a crisp cracker and lick your lips. The kids eat it from a spoon, but the dentist wouldn't approve.

Take a large can of condensed milk and fill a large (8 quart) pot with enough water so about 2 or 3 inches covers the can, which you will place within it. Bring to a boil and keep the heat high enough to maintain a rolling boil for 3 hours. Turn off heat, BUT DON'T REMOVE THE POT. Leave it as is overnight.

The next day, you can remove the top of the can and spoon out a lovely spreadable caramel syrup. To keep, putin a freshly-washed jar or plastic container with cover; refrigerate.