Mix cornstarch and sugar. Add 4 tablespoons butter and half and half. Cook over medium heat, stirring constantly, until mixture boils and becomes thick and creamy. Remove from heat and stir in the vanilla. Preheat oven broiler to high. Pour mixture into pie crust. Drizzle 2 tablespoons butter over top and sprinkle with cinnamon. Put under broiler until butter bubbles and refrigerate for at least 1 hour before serving.
Mix cornstarch and sugar. Add 4 tablespoons butter and half and half. Cook over medium heat, stirring constantly, until mixture boils and becomes thick and creamy. Remove from heat and stir in the vanilla. Preheat oven broiler to high. Pour mixture into pie crust. Drizzle 2 tablespoons butter over top and sprinkle with cinnamon. Put under broiler until butter bubbles and refrigerate for at least 1 hour before serving.
Starch molecules require precise thermal energy to properly hydrate and swell, which creates the thick, spoonable texture characteristic of a successful custard filling. When you combine cornstarch with sugar before introducing the half-and-half, the dry sugar granules physically separate the microscopic starch particles to prevent them from clumping into insoluble lumps upon contact with moisture. Constant agitation over medium heat ensures uniform heat distribution across the bottom of the saucepan, preventing scorching while the amylose and amylopectin chains uncoil and trap the liquid. If the mixture fails to reach a full boil, the starch will not achieve complete gelatinization, resulting in a runny filling that weeps inside the pastry shell.
Direct radiant heat from a high broiler transforms the surface butter and cinnamon dusting into a caramelized glaze within seconds. Because broilers emit intense infrared radiation that heats surfaces unevenly, positioning the pie on the highest oven rack requires undivided attention. Watch the top surface continuously for sixty seconds or less; the high fat content in butter burns rapidly once the moisture evaporates.