Take sugar and maple syrup in a pan on medium heat along with 3 tablespoons of water and stir it for a second or so and then let it cook . Do not stir it with spoon but you can stir the pan of course on heat slightly. Let the sugar caramelize. Once you see it has changed color from light to dark shade, switch off the stove. As we are using maple syrup it would already looking brown, but you should be able to guess it is done when you see the sugar has melted and is thick in consistency.
Take all of the eggs in a bowl and add a pinch of salt to it.You can do this step with the help of a blender or a kitchen aid mixer . And, whisk it thoroughly. Then, add the puree of purple yam. Now, if you find fresh purple yam then remove the skin and roast it on stove and then either boil it and puree it or if they have soften while roasting then you can go ahead and puree them. Either ways it works.
If you are using the frozen puree then directly add it to the eggs and mix everything thoroughly, add vanilla also.
Mix the evaporated milk and condensed milk also this mixture and blend it well. And, then set aside till we assemble the chiffon cake.
Now take egg whites in the bowl of your mixer, add the cream of tartar and let it stand for a minute or so.
In another bowl sift the cake flour, salt and baking powder and add the yolks to it.
At this point preheat your oven at 325F.
Add the oil, milk and lemon zest to it and blend everything well with a hand blender. Beat until everything is well blended.
Now, with kitchen aid attachment, beat the eggs whites slowly and then gradually increasing the speed , when it foams start adding the sugar .Once, in a while stop and check if meringues is ready or not. Once you see soft peaks then fold half of the meringue in the batter. And, then rest of it , and please fold it gently or you might just deflate the whites.
Now, assemble everything together. Place ramekins in a deep dish and pour in the caramelized maple syrup and pour in the purple yam flan mixture and then gently top it off with the cake mixture. The cake batter might float because of its lightness.
Fill the tray in which we have lined the ramekins with steamed water be careful not to drop water in the ramekins or custard.
Place the tray carefully in the oven and bake it for about 20 minutes. After 20-25 minutes check whether it is done or not. You can tap and feel the cake has cooked or not or carefully test with a tooth pick.
Remove the ramekins on a clean towel so that the they can be wiped with the help of towel and are easy to handle. Gently, with the help of a pairing knife or I use frosting spatula for this part, release the edges and invert it on a plate and remove it. But, be careful to release the edges properly and tap the bottom of ramekin while inverting it to the plate for a perfect flan.
You can garnish it with fresh flesh of coconut and serve it directly or may be after sometime chilled.