Preheat the oven to 425°F.
In a large bowl, combine the chopped rhubarb, sugar, flour, salt, and cinnamon. Toss until the rhubarb is well coated.
In another bowl, whisk together the eggs, heavy cream, and vanilla extract until smooth.
Pour the egg mixture over the rhubarb mixture and stir gently to combine.
Pour the filling into the unbaked pie crust, spreading it evenly.
Bake in the preheated oven for 15 minutes. Reduce the temperature to 350°F and continue baking for an additional 30-35 minutes, or until the custard is set and the top is lightly golden.
Remove from the oven and let cool on a wire rack for at least 2 hours before slicing.