Preheat the oven to 425°F (220°C).
In a large bowl, combine chopped rhubarb, sugar, flour, and salt.
Add vanilla extract and lemon juice to the mixture and stir until well combined.
Roll out the pie crust and place it in a 9-inch pie dish.
Pour the rhubarb mixture into the crust, spreading it evenly.
Dot the filling with small pieces of butter.
Cover with another layer of pie crust or create a lattice top.
Trim and crimp the edges of the crust to seal.
Bake in the preheated oven for 15 minutes.
Reduce the temperature to 350°F (175°C) and bake for an additional 30 minutes.