Combine dry ingredients in heavy 4-quart saucepan. Stir in cream. Bring to a bubbly boil on medium heat, stirring constantly. Boil without stirring to 234°F.

Remove from heat, add butter and vanilla. Do not stir. Cool at room temperature to 110°F.

Beat until fudge thickens and loses some gloss. Quickly spread in lightly buttered 8 or 9-inch pan.