1. In small heavy saucepan (not nonstick), stir together 1/2 cup sugar and 3 tablespoons water to dissolve sugar. Bring to a boil over high heat; boil, without stirring, until amber in color, 5 to 6 minutes. Carefully pour into six 1/2-cup ramekins, swirling to coat bottoms and partway up sides.
2. Heat oven to 350 degrees F.
3. In medium-size saucepan, bring half-and-half to a gentle boil. Stir in cinnamon and nutmeg. In large bowl, whisk eggs and yolks with remaining sugar, the liqueur and vanilla. Whisk 1 minute. Slowly stir in half-and-half mixture. Pour into ramekins. Place in roasting pan. Fill pan with boiling water to come halfway up sides of ramekins.
4. Bake in 350 degrees F oven until flans are just set, 30 minutes. Remove ramekins to wire rack; let cool. Refrigerate. To serve, run knife around edge of flans; invert onto plates.