Preheat the oven to 325 degrees. To make caramel: combine the sugar and the water in a medium saucepan. Be sure all the sugar granules are washed down from the sides of the pan (use a wet pastry brush). Cook over moderate heat, swirling the pan occasionally, until the color is golden brown and the mixture smells like caramel. This will take about 10 to 15 minutes. Pour the caramel into a 9 inch round cake pan and, holding the pan with an oven glove, swirl it around to generously coat the bottom and sides. Set aside.
In a large mixing bowl, gently whisk together the eggs, egg yolks, sugar, vanilla, and 2 cups of the half and half, without whisking in any air. Bring the remaining half and half and the port to a simmer in a small saucepan and begin whisking this into the egg mixture a little at a time, whisking constantly until it is all incorporated. Pour through a strainer into the prepared cake pan. Place the pan inside a large roasting pan and pour very hot tap water into the pan so that it comes halfway up the sides of the cake pan. Bake for about 1 to 1 1/4 hours, or until the center is slightly jiggly but not wavy. Cool to room temperature and then cover with plastic wrap with the plastic gently touching the top of the flan. Refrigerate for at least 3 hours and up to 4 days.
To unmold the custard, run a small sharp knife around the inside edges of the dish several times to loosen it. Dip the bottom briefly in a basin of very hot tap water. Invert a round platter over the dish and turn them both over together, shaking the two a little to help release the custard (or rap the bottom of the platter gently on the work surface). The caramel sauce will run out around the edges of the platter. Garnish the top of the flan with violets or other edible flowers.