Whisk sour cream and egg yolk, set aside. Pulse dry ingredients. Add butter and pulse. Add half egg mixture until combined, add remaining mixture, and pulse. Gather together into two balls, wrap with plastic wrap, and refrigerate for 30 min.
In a pan, stir together peaches, brown sugar, cornstarch, cinnamon, vanilla extract, and salt. Simmer on low heat, stirring occasionally until the mixture thickens up.
Roll the dough balls out with a rolling pin until they’re both about 10” around. Place one crust in a 9” pie pan. Fill the crust with the peach filling.