Begin by mixing flour, corn starch, eggs, and sugar. Whisk the ingredients together in a medium sized bowl to later combine. Place a 3 quart pot on low heat and stir in milk for 1-2 minutes, add butter (stir until melted). Add the flour mix into pot and stir until boils (turn up heat if necessary). When the boiling begins add vanilla, stir, and remove from heat. Add cold water and stir, this should cool and make the mix smooth. Pour the pie mix into the shell and sprinkle cinnamon evenly across the top. Place pie into fridge until firm and cool. Once the pie has cooled, serve with whipped cream if desired and enjoy!