Liberally coat a 10-cup (2.5 liter) Bundt pan with cooking spray. Add the cake batter, smoothing out the top with an offset spatula or spoon. Carefully ladle in the flan so you disturb the cake batter as little as possible. Transfer the Bundt pan to a roasting pan or baking dish large enough to fit the Bundt pan. Grease a piece of foil and place it greased side down onto the Bundt pan, folding it over the edges to loosely seal it. Transfer to the oven, then pour water (from the tap is fine) into the roasting pan or baking dish to come up 2 to 3 inches (5 to 7.5 cm).
Bake for 2 hours to 2 hours 15 minutes, checking for doneness after 1 hour 45 minutes, using a skewer inserted into the cake to make sure it’s baked through, with little to no crumbs sticking to the skewer when you pull it out.
Carefully remove the Bundt pan from the roasting pan and let it cool to room temperature before placing it in the fridge to cool completely, at least a couple of hours.
Once you’re ready to serve, carefully run a knife around any edges that are still sticking, then invert onto a serving platter, gently shaking it up and down if it’s being difficult (if it was greased properly, you shouldn’t have any major issues).
If desired, serve with dulce de leche and a sprinkle of chopped nuts or with whipped cream and a sprinkle of cinnamon.