In a 1 quart saucepan, combine the water, sugar and lemon juice (or vinegar). Stir once or twice to combine. Bring to a boil, lower the heat, and simmer without stirring until the syrup turns dark. Be vigilant so that the sugar does not burn.
Pour hot bubbling sugar into a 10” glass pie plate, tilting the dish so the sugar covers as much of the bottom of the plate as possible. Set aside. (You may choose to make your flan in individual serving molds. If so, simply divide the bubbling sugar between 8 heat proof ramekins.)
Fill a pitcher with water and set aside. Find a deep baking pan in which your pie plate will fit (the bottom pan in a broiler pan set works well) Heat your oven to 325°. Adjust the rack in your oven so that one is in the middle.
In a 2 quart saucepan, bring the milk, cinnamon and 1/2 cup of the sugar to a boil, then immediately remove from the heat. Add the chocolate, and allow the mixture to rest and the chocolate to melt, about 15 minutes.
In a separate bowl, beat the eggs, egg yolks, and remaining ½ cup of sugar with an electric hand mixer. One spoonful at a time, add 2 cups of the warm chocolate milk mixture while continuously beating the eggs. Pour egg mixture back into the saucepan of warm chocolate milk. Stir to break up any foam and add the vanilla extract. Pour flan mixture into a large empty pitcher.
Place prepared caramel pie plate in the deep baking pan. Fill the pie plate with the flan mixture. Place the deep baking pan with filled pie plate in the oven, then fill the deep baking pan with water so that water surrounds the flan filled pie plate. Close the oven, and bake the flan for 50 minutes, until a knife comes clean out of the center. (Bake only 35 minutes if you are using individual ramekins) Remove flan from oven and cool completely.
Once cooled, run a knife around the edge of the flan to separate it from the pie plate. Invert the flan onto a platter before serving. Place one Marcona almond on each serving of flan.