Remove frozen crust from freezer and allow to sit for 15 minutes. Transfer to pie dish if desired. Using a fork, add several pokes to the crust.
Preheat oven to 450 degrees.
Using a potato masher, mash yams just until they are no longer whole.
Cream butter and sugar in large mixing bowl.
Lightly whisk eggs. Add to sugar and butter mixture.
Add yams to mixture.
Add cinnamon, vanilla, and flour to mixture.
Beat on low until mixture is well blended.
Pour mixture into 9" pie crust.
Bake at 450 degrees for 15 minutes.
Reduce oven temperature to 350 degrees and continue baking for 50 minutes.
Check for doneness by inserting a wooden toothpick into the center. If it comes out clean, the pie is done. If not, return to oven for 5 minutes.
Allow pie to cool before slicing. Store remaining pie in refrigerator after serving.