1-1/2 teaspoons plus 1/4 cup butter, softened, divided
1 cup packed brown sugar
1/2 cup evaporated milk
2 tablespoons light corn syrup
2-1/2 cups confectioners' sugar
2 cups coarsely chopped salted cashews
Line a 9-in. square pan with foil and grease the foil with 1-1/2 teaspoons butter; set aside.
In a heavy saucepan, combine the brown sugar, milk, corn syrup and remaining butter. Cook and stir over medium heat until sugar is dissolved. Bring mixture to a rapid boil, stirring constantly for 5 minutes.
Remove from the heat. Gradually add confectioners' sugar; mix well. Fold in cashews. Immediately spread into prepared pan. Cool. Using foil, lift fudge out of pan. Cut into 1-in. squares. Refrigerate in an airtight container.