I was tempted to cook the unopened can in boiling water but I was frightened to chance it. I have a friend from church who did this for years. She is from Argentina and this was the way she and her family always did it. But, one day the can exploded and she suffered a serious eye injury.
OVEN METHOD: Pour 1 can EAGLE BRAND® into 9-inch pie plate. Cover with aluminum foil; place in larger shallow pan. Fill larger pan with hot water. Bake at 425ºF for 1 hour or until thick and caramel-colored. Beat until smooth.
STOVETOP METHOD: Pour 1 can EAGLE BRAND® into top of double boiler; place over boiling water. Over low heat, simmer 1 to 1/2 hours or until thick and caramel-colored, stirring occasionally. Beat until smooth.
MICROWAVE METHOD: Pour 1 can EAGLE BRAND® into 2-quart glass measuring cup. Cook on MEDIUM (50% power) 4 minutes, stirring briskly every 2 minutes until smooth. Cook on MEDIUM_LOW (30% power) 20 to 25 minutes or until very thick and caramel-colored, stirring briskly every 4 minutes during the first 16 minutes and every 2 minutes during the last 4 to 10 minutes.
And then I found a SLOW COOKER METHOD:
Use a 4-quart slow cooker. Find an oven-safe dish to insert into your stoneware. You can use individual ramekins or a casserole dish. Carefully pour water all around the dish, until the water reaches three-quarters of the way up the sides of the dish. Open the cans of sweetened condensed milk and pour into the inserted dish(es). Cover and cook on low for 8 hours.
1/2 t salt
Whisk together the flour, baking soda and salt.
Working with a stand mixer, preferably fitted with a paddle attachment, or with a hand mixer in a large bowl, beat the butter at medium speed until soft. Add the 3/4 cup of dulce de leche and both sugars and continue to beat until light and fluffy, about 3 minutes. Add the eggs one at a time, beating for 1 minute after each addition. Don’t be concerned if the mixture looks a little curdled- it will smooth out when the flour mixture goes in. Reduce the mixer speed to low and add the dry ingredients, mixing only until they disappear into the batter.
Spoon the dough onto the baking sheets, using a heaping teaspoon of dough for each cookie and leaving 2 inches between them.
Bake the cookies 10 to 12 minutes, rotating the pans from top to bottom and front the back at the midway point. The cookies should be honey brown with a light sugar crust, but they will still be soft, so remove the sheets from the oven but don’t touch the cookies for another minute or two. Then, using a wide metal spatula, transfer the cookies to a rack to cool to room temperature.
Repeat with the remaining dough, making sure you cool the baking sheets before spooning the dough onto them.
When the cookies are completely cool, spread the flat bottoms of half the cookies with a small amount of dulce de leche, and sandwich with the flat sides of the remaining cookies.
Makes about 30 sandwich cookies