Generously spray a 9-by-12-by-2-inch pan with cooking spray; line it with parchment and butter the top of the parchment.
In a large saucepan, mix the brown sugar, granulated sugar, corn syrup and 1 cup of the cream. Heat until the mixture begins to boil. Slowly stream the remaining 1 cup cream into the mixture, stirring while it's boiling. Attach a candy thermometer to the pan and cook the mixture over medium heat until it reaches 244 degrees F. Remove the pan from the heat and add the butter, chopped pecans and vanilla. Pour the candy into the prepared pan. Cool the candy in the refrigerator until it is just firm but not hard, about 1 hour.
Cut the candy into 1-inch squares. Cut waxed paper into 4-inch squares and wrap each piece of candy individually. Store in the refrigerator. Remove the candy from the fridge and allow it to soften slightly before serving.