Preheat the oven to 450 degrees F (230 degrees C).
Separate egg yolks and egg whites. Set egg whites aside for meringue.
Place rhubarb into the prepared pie crust. Mix sugar, evaporated milk, 3 egg yolks, flour, and salt for filling together in a bowl. Pour mixture over rhubarb. Place pie onto a cookie sheet.
Bake in the preheated oven for 12 minutes. Turn oven temperature down to 350 degrees F (175 degrees C), and bake for 30 minutes more. Remove pie from the oven. Lower oven temperature to 325 degrees F (165 degrees C).
Beat the reserved egg whites for meringue in another bowl until frothy. Slowly add sugar, salt, and cream of tartar. Beat until stiff peaks form. Spread over the baked pie.
Bake in the preheated oven until light golden brown, about 15 minutes. Cool slightly before serving.