Fannie Farmer's Chocolate Fudge

2 tablespoons butter
4 cups granulated sugar
2 teaspoons vanilla extract
1 1/2 cups light cream
4 squares chocolate
1/4 teaspoon cinnamon

Melt butter in a pan, add sugar, cream and chocolate, stir gently until chocolate melts. Boil without stirring to 238 degrees F or until mixture forms a soft ball when dropped into cold water. Remove from heat, let stand until cool and add flavoring. Beat with a wooden spoon. Pour 3/4-inch thick into a buttered pan and mark in squares.