This is my Nana Jackson's recipe. We make them every Christmas. We've given them as neighbor gifts, sent them to missionaries and enjoyed eating the edges when we wrap them. These are one of my favorite Christmas traditions....
1/2 can sweetened condensed milk
3 cups regular whipping cream (NOT Heavy whipping cream)
2 cups white sugar
2 cups white corn syrup
pinch of salt
2 tsp. vanilla
Mix sweetened condensed milk and whipping cream together in a double boiler, placed over a pan of about 2-3 inches of boiling water. Prepare a 10 x 13" glass pan by greasing the bottom and sides with about 1 Tablespoon of softened butter. Set aside.
In a large heavy pot, stir together sugar, corn syrup and salt. Cook on medium heat until boiling. Add 1/2 cup of the cream mixture to the syrup mixture and stir well. Continue adding 1/2 cups of cream every 3-5 minutes, stirring often. This process will take about 30-40 minutes. Caramels will begin to deepen in color and thicken in consistency. When all the cream has been added, measure caramel temperature with a candy thermometer and cook until caramels reach 232*** (SEE NOTE BELOW) degrees (but not to soft ball stage). To check, you can take the caramels off the heat and drop a ball of caramel into a cup of cool water to check consistency. If it's still too sticky and soft, continue cooking a little longer, but be careful not to go past the soft ball stage, or caramels will be hard. Remove from heat and stir in 2 tsp. vanilla. Pour into buttered pan, but don't scrape the edges of the pan too much. Scrape the caramel that sticks to the sides of the pan with a spatula into a small bowl, because this tends to be harder than the rest of the caramel. (This is great to give the kids spoonfuls, when cooled:-). Let caramels set for 10-12 hours, then cut into squares and wrap in waxed paper. Makes about 100.
***We've lived at sea level and I had to cook them to 250° there. Now we're at 5200 feet and I only need to cook them to 230°. If, for some reason, your set caramels still seem too soft, you can put them back into a pan and re-heat them to a little higher temperature. I've only had to do this once, but it works:-)