To make the pie crust:
Combine the flour, sugar, and salt in a bowl. Add the cubed butter and toss to coat. Cut the butter into the dry ingredients with a fork or a
pastry blender until butter is the size of peas.
Add 3 tablespoons of the cold buttermilk and use a spoon and then your hands to stir the mixture until it comes together into a ball. Add more buttermilk as needed to bring it all together.
Shape dough into a disk and cover with plastic wrap. Chill in the fridge for at least 1 hour and up to 5 days. Dough can also be frozen (double-wrapped) for up to 2 months.
To assemble the pie:
Preheat oven to 400°F.
Let the crust dough rest at room temperature for five minutes. On a lightly floured surface, use a rolling pin to roll out the dough into a rough 12 inch circle. Dough should be about ¼ inch thick. Transfer dough to 8 or 9-inch cast iron skillet or any greased round baking dish.
In a medium bowl, toss the sliced strawberries, sugar, cornstarch and vanilla. Dump into the pie crust and spread filling evenly into the pan. Fold the overhanging pie crust over the filling.
Beat the egg and water together and brush over the pie crust. Sprinkle with sugar, if desired.
Bake until crust is golden and filling is bubbling, about 1 hour. Let cool at least 30 minutes before serving. To let the filling completely set (so filling isn't runny), let the pie cool completely before slicing. Store leftovers in the fridge for up to 3 days.
Calories: 175kcal, Carbohydrates: 23g, Protein: 2g, Fat: 8g, Saturated Fat: 5g, Cholesterol: 34mg, Sodium: 108mg, Potassium: 116mg, Fiber: 2g, Sugar: 9g, Vitamin A: 270IU, Vitamin C: 35mg, Calcium: 20mg, Iron: 1mg