Prepare the filling by trimming and slicing fresh rhubarb into 1/2-inch pieces. In a mixing bowl, whisk together flour, sugar, cinnamon, and vanilla extract. Toss the rhubarb with the mixture and let sit for 15 minutes.

Make the pie crust by rolling out the bottom layer on a floured surface to fit your pie plate. Preheat your oven to 450°F (232°C) and place the rolled-out crust into the pie plate.

Assemble the pie by spooning the rhubarb mixture into the crust, dotting the top with pieces of butter.

Create a lattice top by rolling out the remaining crust and slicing it into strips. Weave the strips over the filling and crimp the edges of the pie.

Bake the pie on a baking sheet at 450°F (232°C) for 10 minutes, then reduce the temperature to 350°F (175°C) and bake for an additional 30-50 minutes until bubbly and golden.

Cool the pie on a wire rack for 3-4 hours before serving to allow the filling to set.