Preheat oven to 350. Place piecrust in oven for 10-15 minutes until bottom of piecrust is partially baked. Remove from oven and sit out.
Mix the sugar and cornstarch together until blended. In a small saucepan, melt the butter and heavy cream over medium heat, stirring continuously. Slowly add cornstarch mixture. Let this simmer until it has thickened.
Remove from heat and add vanilla.
Pour mixture into piecrust smoothing out with a spoon or spatula.
For the topping, melt the other 4 tablespoons of butter and add the 1/2 cup of sugar until the sugar is dissolved.
Remove from heat and add cinnamon.
Drizzle over pie, completely covering.
Place on cookie sheet and bake for approximately 25 minutes.
Turn broiler on for 1 minute watching pie carefully, then remove.