2 cups (16 oz/450g) sugar
3/4 cup (6 fl oz/170ml) water
1/4 teaspoon cream of tartar (there is no substitute for this)
2 teaspoons lemon juice*
a pinch of salt
In a heavy bottomed saucepan, over medium heat, add the sugar, water, cream of tartar and lemon juice.
Once the sugar dissolves, turn down the heat and let the syrup simmer steadily until it reduces significantly and becomes a thick syrup that drips off your spatula slowly. This will take roughly 15 to 20 minutes. You can test if it's ready by putting a drop on a cold plate and placing it back in the fridge for 10 minutes. If it is really thick once it's cold then it is ready. To be even more exact, you want it to reaches 230°F on a candy thermometer.
Remove from the heat and put the pot in a bowl of cold water to cool it down quickly. Once the syrup cools down completely use as directed in your recipe.
You will end up with roughly 1 1/3 cups (14oz/398g) of corn syrup substitute. Store in an airtight container at room temperature for 3 months.