3 cups brown sugar
1 cup evaporated milk
2 tablespoons light corn syrup
1 teaspoon vanilla
1 cup chopped nuts, optional
3 tablespoons butter
Butter the sides of a medium saucepan (2 to 3-quart size). Add the brown sugar, evaporated milk, and corn syrup; bring to a boil, stirring constantly. Continue boiling, stirring frequently, to soft ball stage or when candy thermometer registers about 235 F.*
Remove from heat and drop the butter onto the mixture, but do not stir. Let cool (without disturbing) until it registers about 120 F on the candy thermometer. This will take about 25 to 35 minutes. Add the vanilla and beat with a wooden spoon until the fudge just begins to thicken and loses its glossiness. You could also transfer the mixture to a stand mixture and beat with the paddle beater.
Add chopped nuts and beat for a few more minutes, until it is thick but not hardening. Pour or spread in a greased pie plate or 8-inch square pan.
Score when set and cut into squares when firm.