Preheat your oven to 350°F (175°C).
In a saucepan over medium heat, melt the sugar until it turns into a golden caramel. Pour the caramel into a baking dish and let it cool.
In a blender, combine the evaporated milk, sweetened condensed milk, eggs, pumpkin puree, vanilla extract, ground cinnamon, and ground nutmeg. Blend until smooth.
Pour the pumpkin mixture over the cooled caramel in the baking dish.
Place the baking dish in a larger pan filled with hot water. Bake in the preheated oven for about 60 minutes, or until a knife inserted in the center comes out clean.
Let the flan cool to room temperature, then refrigerate for at least 4 hours before serving.
To serve, run a knife around the edges of the flan, invert onto a plate, and enjoy!