Step 1

Line an 8-inch square pan with foil, then grease the foil with 1 teaspoon butter.

Step 2

In a large, heavy saucepan, combine the remaining butter, the granulated and brown sugars, the whipping cream and the salt. Bring this blend to a rapid boil over medium heat, stirring constantly. Then, once it boils, cook it without stirring until a candy thermometer reads 234°F. (This is the soft-ball stage.) Remove the pan from the heat and add the vanilla to the pan, but do not stir.

Step 3

Cool the blend, without stirring, to 110°, which will take about 30 minutes. Then beat the mixture with a spoon until the fudge just begins to thicken. Next, gradually stir in the confectioners' sugar, mixing until the fudge is smooth. Add the nuts and continue stirring until the fudge becomes very thick and just begins to lose its sheen. Immediately spread it into prepared pan and let it cool to room temperature.

Step 4

Using the foil, lift the fudge out of pan, then remove the foil and cut the fudge into 1-inch squares. Store fudge pieces between layers of waxed paper in an airtight container.