In a small, heavy skillet, combine the coriander, cumin, and cardamom seeds and saffron. Heat over a medium flame, shuffling the pan frequently, to toast the spices until they are fragrant and start to pop, 30 seconds once the pan is hot.
Meanwhile, stir together the sugar with the boiling water until dissolved (or mostly 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 (preferablchill the syrup until cold, at least 1 hour and up to several days.
Make the mules:
In a shaker or jar, stir together the vodka, ginger syrup, and lemon juice for 30 seconds. Strain into a highball glass filled with ice, top off with sparkling water, and top with a mint sprig. Taste, adding more lemon or syrup if you feel the drink needs it. Enjoy immediately.
Inspired by ABV.Nutritional values are based on one drink.