Don't know about Rudy's but here is my recipe.
Buttermilk Pie
½ c. butter, melted
3 eggs, beaten
1 c. buttermilk
1 tsp. vanilla
1 c. sugar
2 tbsp. all purpose flour
¼ tsp. salt
One pre-baked 9” pie shell.
Preheat oven to 325*
Mix together butter, eggs, buttermilk, and vanilla. Add sugar, flour, and salt and mix well. Pour into pre-baked pie shell. Bake until pie is set but slightly jiggly in center (it will continue to cook after coming out of the oven), about 25 minutes.
Serve with fresh, seasonal berries. Cool Whip optional.
If you want my piecrust recipe I'll dig it up.