Step 4: Prepare the Syrup
Pour the water down the sides of the pan. This will wash down any errant flecks of sugar.
Heat on a medium-high burner until the temperature of the syrup reaches 246 F (119 C) for unsweetened liquors, or 243 F (117 C) for sweetened liquors. Yes, that three degree difference really does matter. If crystals have formed on the side of the pan, wash them down with a silicone pastry brush dipped in cold water.
When the required temperature has been reached, remove the saucepan from the heat. Add the liquor, which has been warmed in the microwave. Just make it warm to the touch, no need to boil it.
Stir the solution gently until all of the liquor has been incorporated.
If you agitate the solution too much at this point you can induce crystallization, which will ruin all the work you've done. Just stir the solution in - slowly - with the plastic spoon.
Once it's all mixed, you can fill the molds.