In medium bowl, whisk together 1 cup milk, egg, egg yolk and cornstarch until smooth. Whisk in remaining milk, pumpkin and spices. Set aside.
In large saucepan, melt butter over medium heat.
Add brown sugar and cook until sugar begins to melt, stirring or whisking frequently, about 4 minutes. Whisking vigorously, slowly add about 1/2 cup of the milk mixture until combined, then gradually stir in another 1/2 cup. Add the rest of the mixture and bring to a simmer, stirring constantly. (once fully blended, you can raise heat slightly to medium/medium-high). Bring to a heavy simmer and cook for 1 to 2 minutes or until thickened.
Remove from heat and stir in vanilla.
If desired, strain pudding before pouring into dessert glasses.
Cover with plastic wrap and chill 2 to 3 hours,
Serve with whipped cream.
Light or dark sugar may be used according to preference - dark sugar will result in a slightly darker pudding and a subtle stronger butterscotch flavor, while the light brown sugar is lighter in color as well as flavor.