To make caramel, in a small heavy saucepan melt 3/4 cup of sugar over low heat, stirring constantly. After it melts, increase to heat to medium and cook, without stirring, until it turns dark gold. Be careful not to burn.
Remove from heat and add water (it may hiss at you.) Return to low heat and stir until liquid. Carefully pour into small pie or cake pan, tilting until the bottom and part of the sides are coated. Put aside.
Pre-heat oven to 325 °F (160 °C). Whisk 1/3 cup sugar and eggs until smooth. Mix in puree, cinnamon and vanilla. Stir in milk.
Put the caramel-coated pan into a larger pan. Pour cold water into the larger pan so that the water comes to about halfway up the sides of the smaller pan.
Pour the pumpkin mixture into the caramel-coated pan. Place in pre-heated oven.
Bake for an hour, until a knife inserted a little bit away from the edge of the pan comes out clean.
Remove carefully from oven, place in sink for best control. Drain the water. Remove custard pan from the larger pan and place on rack to cool. Refrigerate after cooling until ready to serve.
To serve, place a larger plate or platter over the pan and invert. Cut into eight pieces.
There are 170 calories in 1 serving of Pumpkin Flan.