Bring sugar and water up to a light simmer and cook until all of the sugar is dissolved. Add ginger and steep for 30 minutes. Pour ginger-simple syrup into blender and puree. Strain out pulp and store in a tightly sealed jar or bottle. Will keep for several weeks in the refrigerator.
Pour some bar sugar onto small plate and grate a pinch of nutmeg on top, mix well.
Add tequila, lime juice, 5 ounces ginger-simple syrup and ice to cocktail shaker and give it a good shake. Run lime wedge around rim of glass and dip in sugar/nutmeg mixture, add ice and pour in contents of shaker, grate a little nutmeg on top and serve with a wedge of lime.