Place the sugar and water in a saucepan and stir to combine. Bring it to a boil, stirring regularly to prevent burning until the sugar is dissolved. Stir very gently to prevent sugar water from splashing up the sides of the saucepan. Once boiling gently stir in the lemon juice or citric acid. Reduce the heat to a very low and gentle simmer (I use "3" on my induction cooktop but this will vary from cooktop to cooktop) Leave the saucepan uncovered. DO NOT STIR the syrup again. Let it simmer on very low for 40-60 minutes or longer until the sugar is a rich amber color. If you're using a thermometer the temperature should be about 240-250 degrees F.Note: If your syrup is too thick and stiff you can reheat it, adding a little bit of water. If your syrup is too runny then you need to let the syrup caramelize longer.
Turn off the heat, let it sit for a few minutes, then pour the hot syrup into a glass jar and let it cool completely before closing the jar with tight sealing lid.Store your golden syrup at room temperature where it will keep for several months. This makes approximately 3 cups of golden syrup.