Preheat oven to 350 F
Grease pie plate with unsalted butter, set to side
Whisk eggs, essence and sugars to combine well
Whisk in 1 c of flour, then whisk in the last cup, until completely combined
Whisk in 1 c of heavy cream, then whisk in the last cup, until super smooth
Fold in sliced rhubarb
Pour batter into pie plate, sprinkle top with flour lightly, then sprinkle with cinnamon sugar
Bake for 45 mins
Cool for an H or two on room temperature, slice and serve