1. Preheat oven to 400 degrees Fahrenheit (200 degrees Celsius).
2. Slice peaches thinly and arrange in circles around the pie crust.
3. In the bowl of a mixer, beat sour cream, egg yolks, sugar, flour, and vanilla until combined. Pour over peaches and bake for 25-30 minutes or until cream is beginning to set.
4. Meanwhile, prepare topping. In a small bowl, combine all streusel ingredients until mixture resembles crumbs.
5. After pie has baked, sprinkle streusel topping evenly over the peaches and cream. Return pie to oven and bake 15 minutes longer or until streusel is golden. Cool before serving.
6. Pie can be served warm, room temperature, or straight from the fridge. Garnish with nectarine slices arranged in a circle, in the center of the pie. Sprinkle with cinnamon, if desired.
You can make your own pie crust as follows: 1 cup flour, 1/4 teaspoon salt, 1/3 cup margarine (75 grams), 1 and 1/2 teaspoons vinegar, and 2-3 tablespoons soy milk. Simply combine all ingredients, aside from soy milk, in a food processor with the knife attachment or in the bowl of a mixer. Add milk gradually until a ball forms, or dough comes together. Place in a plastic bag and refrigerate for 30 minutes. I baked it in a fluted tart pan with removable bottom.