Cook milk in a small nonaluminum saucepan over medium-low heat, stirring once, 2 to 3 minutes or just until bubbles appear (do not boil); remove from heat. Add next 3 ingredients. Cover and steep 20 minutes. Remove and discard tea bags, without squeezing; discard mint sprigs and lemon quarters. Reserve 1 cup tea mixture.
Whisk together sugar and eggs in a large bowl until mixture is thick and pale yellow. Gradually whisk in reserved 1 cup tea mixture and half-and-half until well blended. Pour mixture into 6 (4-oz.) custard cups or ramekins. Place custard cups in a roasting pan; add hot water halfway up sides of cups.
Bake at 300° for 40 to 50 minutes or until a knife inserted in center of custard comes out clean. Carefully remove from oven, and let stand in pan in water bath 30 minutes. Remove from water bath. Serve immediately, or cover and chill at least 2 hours. Garnish, if desired.
Note: Nutritional analysis does not include garnishes.