For candied zest: combine sugar with 2 tablespoons of water in a pan and heat up. Cook, stirring occasionally, until sugar has completely dissolved. Bring to a boil and cook until syrup takes on a pale caramel color. Add orange zest and stir so that zest is well coated with caramel. Simmer for about 5 minutes on low heat. Remove from the pan and drain in a sieve.
For the creme caramel: whisk sugar with egg yolks until creamy. Combine milk with slit vanilla bean and bring to a boil, add hot milk to egg mixture.
For the caramel base: combine sugar with water in a small pot and simmer until sugar is golden brown. Immediately pour about 3 mm (approximately 0.1 inch) of caramel into very lightly oiled ramekins. Strain creme through a sieve into ramekins. Fill large casserole with about 2 cm (approximately 3/4 inch) of hot water, place ramekins into casserole and bake in preheated oven at 180°C (approximately 350°F) for about 30 minutes. Remove from oven and let cool in ramekins. Invert creme caramel onto plates and garnish with candied orange zest. Serve.