In sauce pan combine first 4 ingredients. Bring to boil.

In another sauce pan combine brown sugar and cornstarch.

Gradually whisk in hot mixture into brown sugar mixture.

Add butter.

Cook over medium heat, whisk constantly, 5-10 minutes or until thick.

Simmer 1 minute and stir in vanilla.

Pour into par baked pie shell and sprinkle with cinnamon.

Bake at 375 for 25 minutes.