Preheat oven to 350 F (180 C). To make caramel, heat sugar and1/4 cup ( 50 mL) cold water in a saucepan over medium high heat. Stir only until the mixture starts to boil. Once the sugar becomes caramel coloured, quickly add 1/3 cup (75 mL) cold water. Continue cooking 30 seconds. Pour three quarters of the caramel into a round 8 inch (20 cm) baking dish. With a wooden spoon, spread it out evenly using a circular motion. Reserve the rest of the caramel. In a stainless steel bowl, beat sugar, eggs, egg yolks and Tia Maria, if using. Do not allow the mixture to become foamy. In another bowl, beat the melted chocolate with the hot milk. Incorporate into the egg mixture, beating continuously. Pour the mixture through a strainer into the baking dish, over the caramel. Place in a baking dish filled half-full with hot water. Bake 45 minutes.
Remove from oven and cool before refrigerating. Serve slices of flan with reserved caramel.