2 cups heavy cream
1/2 cup sweet and condensed milk
2 cups corn syrup
2 cups sugar
1/2 cup (1 stick) butter
1. Scald cream and condensed milk over medium heat. Set aside.
2. In a heavy pan, bring sugar and corn syrup to a boil on high. Boil covered for two minutes.
3. Reduce heat to medium/medium-lowish and stir in butter.
4. Spend 3o minutes slowly adding cream mixture to sugar mixture a ladleful at a time.
5. Simmer until mixture reaches the firm ball stage Use a candy thermometer and the cold water test. On my thermometer, in high altitude, firm ball stage is about 225-230 degrees. (Traditionally, firm ball stage is 240 degrees, so it's important to do the cold water test.) To perform a cold water test, drop a spoonful of the mixture in ice water. When you remove the mixture, it should form a firm ball, one that won’t lose its shape when you take it out of the water, but remains malleable and will flatten when squeezed.
6. Pour mixture into a greased 9 x 13 pan. Let set for several hours. Cut and wrap in wax paper.