Combine sugar, whipping cream, and molasses in a small Dutch oven; cook over medium heat, stirring constantly, until sugar dissolves and mixture comes to a boil. Cover and continue to cook over medium heat 2 to 3 minutes to wash down sugar crystals from sides of pan. Uncover and cook, stirring occasionally, until mixture reaches soft ball stage (238°).
Remove from heat; add butter and vanilla (do not stir). Cool to lukewarm (110°). Beat with a wooden spoon until mixture thickens and begins to lose its gloss; pour into a buttered 8- inch square baking pan. Cut into 1-inch squares.