Neatly line the base and sides of a 20x30cm baking tin with baking parchment. Tip the sugars, cream and butter into a large heavy-based deep saucepan and heat gently, stirring occasionally until all the ingredients have come together and the sugars and butter have melted. Place a sugar thermometer or digital cooking thermometer in the pan, turn up the heat and boil everything together vigorously without stirring until the temperature reaches 125C. Remove from the heat and stir in the vanilla. Leave for a moment for any bubbles to settle, then carefully pour the molten toffee into the prepared tin, swirling the tin until the toffee covers the base. Leave the toffee for at least 2hrs to set – overnight is ideal.

Use the parchment to lift the set toffee out of the tin and cut into squares or fingers. If the toffee is sticking to the knife, lightly oil the blade. Wrap the toffees in waxed paper and store in a jar for up to two weeks at room temperature or a month in the fridge.