In a heavy saucepan combine the sugar, brown sugar, and cream and bring to a boil. Cook on medium heat to softball stage (238 degrees F), then add the butter and pecans. Continue cooking until hardball stage (245 degrees F). Spoon large dollops of it onto a silicone mat or parchment lined baking tray. The pralines will spread and crystallize as they cool.
Recipe courtesy of Gale Gand