2 1/2 cups granulated sugar (625 ml)
2/3 cup light corn syrup (150 ml)
6 tbsp water (90 ml)
2 tbsp baking soda (30 ml)
2 tsp vanilla (10 ml)
Christine's Sponge Toffee
Grease a 9 by 13-inch pan with vegetable oil. Line the bottom and sides of the pan with parchment paper, making sure the parchment sides are at least 2 inches above the sides of the pan. Grease the parchment paper with a little more oil.
Add sugar, corn syrup and water to a deep, heavy bottomed saucepan. Bring the mixture to a boil, without stirring and cook until hard crack stage: when the temperature on a candy thermometer reads 300 degrees F. This should take about 10 minutes. During the cooking process, if there are any sugar crystals on the sides of the pan, brush the sides of the pan with a clean pastry brush dipped in water.
Remove from heat and working quickly, add the baking soda, whisking to incorporate. The mixture will bubble up quite a bit when you add the baking soda so be very careful not to touch the hot toffee. Immediately pour into the prepared pan. Let cool and set completely before touching. Break into pieces and serve. Store at room temperature in an airtight container.