In a medium pot, stir together milk, cream, and cinnamon cereal. Let sit at room temperature for 20 minutes. Strain and discard cereal. The cereal will absorb some of the liquids. Measure liquid. Add enough cream until mixture is a total of 3 cups. Add 1 tablespoon sugar to pot and bring to simmer.
Meanwhile, in a large bowl whisk remaining sugar, cinnamon, and yolks. Once milk mixture begins to simmer, lower heat.
Temper hot milk into sugar-yolk mixture. Slowly add hot milk into yolks about 1/4 cup a time, whisking to distribute heat. Once all the milk has been added to yolks, transfer everything back into the pot.
Stir over medium-low heat until mixture reaches nappe consistency, or 180 degrees F on a kitchen thermometer. Let mixture sit at 180-185 degrees F for 3 minutes to pasteurize egg yolks. Remove from heat. Transfer to an airtight container and let mixture mature in the fridge overnight, or for at least 4 hours.
Freeze mixture in ice cream maker according to your unit's instructions. Once the volume has increased by half and has reached a soft serve consistency, turn off ice cream maker. Pour cinnamon ice cream into prepared pie crust. Cover with plastic wrap and freeze for at least 5 hours.
Before serving, top cinnamon ice cream with whipped cream. Add cinnamon cereal to garnish. Serve immediately.