3 tablespoons light corn syrup
1 cup sugar
3/4 cup dark brown sugar
3/4 cup milk
1/4 teaspoon salt
1 pinch baking soda
2 tablespoons butter, cubed and chilled
6 tablespoons creamy or crunchy peanut butter
1 teaspoon vanilla
Line a 13 x 9-inch pan with plastic wrap or wax paper, leaving the edges hanging over the sides of the pan so that you may lift out when fudge has cooled; set aside.
In a medium saucepan, combine milk, sugars, corn syrup, salt, and baking soda. Bring to a boil over mid-high heat, stirring frequently. Cook until it reaches 236 degrees on your candy thermometer, but don’t over-cook. Remove saucepan from heat immediately and stir in the butter; then add peanut butter and vanilla. Continue stirring until smooth. Pour mixture into prepared pan. Set aside and let fudge set. When fudge is set, lift paper from pan with the fudge, cut into squares, store in sealed container or wrap with freezer paper and twist ends.