1. Preheat oven to 350° F.
For the Filling:
1. Cook the buttermilk, rhubarb and 1 cup of sugar in a large pot over medium heat until the rhubarb is tender. Next, stir in ¼ cup sugar, cornstarch, eggs, cream and salt. Add a few drops of red food coloring if desired. Allow to cool slightly.
2. Pour the filling into the prepared pie crust.
For the Meringue:
1. Using a stand mixer with a whisk attachment or handheld mixer, beat the egg whites and salt until frothy. With the mixer still running, gradually add the sugar. Once all of the sugar has been added, continue to beat the egg whites into firm, glossy peaks.
2.Pour the finished meringue over the pie filling and spread out to the edges. Bake in a 350°F oven for 13 – 15 minutes.