Cut a lemon in half and squeeze out its juice.
Add your water and sugar to a pot and cook it over medium heat. Gently stir the pot (if necessary) to help dissolve the sugar.
Bring the mixture to a boil, then pour your lemon juice through a strainer onto the pot, give it a quick stir to mix the lemon juice with the sugar liquid, and then reduce the heat to medium-low. Do not stir the pot anymore when it begins to boil because it can cause the sugar to crystallize.
Let the pot cook on medium-low to low heat until it turns into a golden amber color and the temperature reaches around 116-117°C (240-242°F). This took me about 1 hour and 45 minutes, but the time may be different for you.
It is highly suggested that you use a thermometer to measure the temperature during the cooking process to ensure that you don’t under- or overcook the golden syrup. No, actually, you do really need one!
Occasionally, wet a brush and brush the sides of the pot where the sugar syrup has splashed to prevent the sugar syrup from crystallizing and falling back into the sugar syrup.
Once the temperature of the golden syrup reaches at least 116°C and the color has turned into a golden amber color, turn off the stove and pour the golden syrup into a container or bowl or just leave it in the pot to cool down. The color will continue to darken while cooling down. Once the golden syrup has fully cooled down, pour it into an airtight glass jar and store it at room temperature away from the sun.