The addition of lemon juice or tartaric acid not only makes the sugar softer, it also delays the caramelization process, allowing more time to properly melt all of the sugar.
Fill a bowl that is large enough to hold the pan used for cooking the sugar with enough cold water to reach halfway up the sides of the pan. Set the bowl aside.
Place the sugar and lemon juice in a copper or stainless-steel pan (see Note). Cook over low heat, stirring constantly, until the sugar is completely melted.