Boil the brown sugar and water in a saucepan, stirring continously until the sugar is melted and turns golden brown. Pour the syrup into flan molds, make sure the whole surface is covered. Set aside to allow the caramel to harden.
Gently combine all the custard ingredients in a large bow, first the eggs, condensed milk, fresh milk, sugar and vanilla. Strain gently into the caramel-lined flan molds.
Cover with aluminum foil and place in a bain-marie. Bake in the preheated oven 160°C (325°F) for 60 minutes or until the mixture is firm. Cool and refrigerate for 4 hours before serving. Overnight is the best.
