Prep: Preheat the oven to 350°F.
Make the caramel: In a small saucepan, add the granulated sugar and water. Stir gently to saturate all the sugar but try not to get any sugar up the sides of the saucepan. Heat on medium heat until the sugar dissolves and it comes to a simmer. Do not stir it after it begins to simmer otherwise it can crystallize.
Pour into pan: Turn the heat to medium-high heat and boil for 10-15 minutes or until it becomes slightly golden. Turn the heat off and gently swirl the pan until it deepens in colour and becomes amber in colour. Immediately pour this into an 8" cake pan and tilt the pan around until it coats the bottom of the pan (use oven mitts as the pan will become very hot). Set aside to let harden.
Custard mixture: In a large mixing bowl, add the eggs, pumpkin puree, condensed milk, evaporated milk, pumpkin pie spice and vanilla extract. Whisk until smooth and combined.
Fill pan: Pour the custard mixture through a fine mesh sieve into the pan on top of the hardened caramel.
Water bath: Place this pan into a larger baking pan and fill it with hot water until it reaches halfway up the cake pan.
Bake: Bake for about 1 hour or until a toothpick in the middle comes out clean and the top is not sticky to the touch.
Chill: Let the flan cool completely on a wire rack at room temperature. Cover and chill in the fridge for at least 4 hours or overnight, preferably.
Release flan: When releasing the flan from the pan, submerge the bottom of the pan in hot water for 5-10 minutes if it has been in the fridge to soften the caramel. Run a sharp paring knife around the edge of the flan. Place a serving plate or sake stand with a rim on top of the pan and flip them both upside down while holding them firmly. Give the top of the pan a few pats and you should hear the flan separating from the pan onto the plate.