Chill the glass: Fill a martini glass with ice and water and let it sit while you prepare the drink. Discard the ice water before pouring.
Shake the Ingredients: Fill a cocktail shaker with ice. Add the Thai tea concentrate, tequila, coffee liqueur (if using), and sweetened condensed milk. Shake vigorously for about 10–15 seconds until well chilled.
Strain and Pour: Strain the mixture into the chilled martini glass.
Garnish and Serve: Garnish with a star anise, a cinnamon stick, or a sprinkle of ground cardamom for an aromatic finish. Serve immediately and enjoy!