Add granulated sugar and stir until fully dissolved.
Add dark brown sugar and stir until fully dissolved.
Reduce the heat and stir until it simmers, let simmer for 5 minutes.
For a thicker syrup, continue to simmer for 10 more minutes.
Remove from heat and add maple extract.
Let cool until thickened.
Enjoy right away or store in an air-tight jar.
Notes
I have tested it many times and this method has proven not to crystallize. Crystallization occurs when sugars do not completely dissolve. If there are any granules of sugar, the sugar molecules will begin to attract other molecules and form crystals.