In a small, heavy skillet, combine the coriander, cumin, and cardamom seeds and saffron. Heat over a medium flame until they are fragrant.
Meanwhile, stir together the sugar with the boiling water until dissolved. Add the syrup, toasted spices, and ginger to a blender and blend until fairly smooth.
Strain the syrup through a very fine mesh strainer, pressing on the solids to extract the good stuff.
Use immediately or preferably chill the syrup until cold, at least 1 hour and up to several days.
For Mules, stir together the vodka, ginger syrup, and lemon juice for 30 seconds. in a shaker or a jar.
Strain into a highball glass filled with ice, top off with sparkling water, and top with a mint sprig.