Dolly Parton has turned up the heat with her latest endeavor. The country music legend’s recent partnership on a cake mix line with Duncan Hines was an instant sellout. On Wednesday, a limited-edition $40 baking collection (comprised of coconut and banana cake mixes, two kinds of buttercream frosting and accessories including recipe cards) dropped on the brand’s website and were sold out before noon. Some 1,400 kits went on sale for the sneak peek. Customers who want to in on the “9 to 5″ hitmaker’s line of cake and frosting mixes inspired by Southern recipes can sign up online to be notified …