If you don't have a thermometer, there are a few ways you can tell if the vegan toffee mixture has reached the correct temperature. For starters, you'll need to keep an extra close eye on the mixture, stirring often to prevent burning. You'll be able to tell it's getting close to the correct temperature when you lift some of the toffee and let it drip back into the pot – if it doesn't immediately reincorporate and instead piles up a bit before melting back into the mixture, it should be close to the correct stage. To confirm it's ready, fill a glass with cold water. Drop a small amount (~1 teaspoon) of the mixture into the cold water. If it gathers into a ball, it's not ready. If it forms flexible, yet not brittle threads, it's at the correct stage. Note that you'll need to use a new glass of water each time you do a new test.