Preheat oven to 375°C (Gas Mark 5).
In a medium saucepan, sauté onions, carrots, potatoes, celery and rosemary in butter until tender. Stir in flour and seasonings. Slowly whisk in broth and simmer until thick, about 30 seconds.
Stir in turkey, peas and Chobani. Pour mixture into 9½-inch pie plate.
Place piecrust over filling. Trim, seal and flute edges of pastry and score top to vent. Brush crust with egg wash.
Bake potpie until golden brown, about 45 minutes, rotating pan midway through cooking. Let stand 10 minutes before slicing and serving.