Molasses Sponge Candy

Directions

1. 1
   Line bottom and sides of a 13- by 9-inch baking pan with foil, then butter foil.
2. 2
   Bring sugar, water, butter, and cream of tartar to a boil in a deep 3-quart heavy saucepan over moderate heat, stirring until sugar is dissolved, then wash down any sugar crystals with a pastry brush dipped in cold water.
3. 3
   Boil without stirring until syrup registers 265F (hard-ball stage) on a candy thermometer, about 10 minutes.
4. 4
   Add molasses (don't stir) and continue to boil undisturbed until syrup registers 295F (hard-crack stage), 4 to 5 minutes.
5. 5
   Remove pan from heat and sift baking soda over syrup, then whisk to incorporate.
6. 6
   (Use caution: mixture will bubble vigorously.)
7. 7
   Immediately pour syrup into lined baking pan and cool completely.
8. 8
   Lift candy in foil from pan, then discard foil and break candy into pieces.