Line 9" pie plate with one unbaked pie crust. Place in refrigerator while preparing filling.
Combine sugar, cornstarch, and salt in large bowl. Add cherries and spinkle vanilla over the top. Toss cherries and sugar mixture until fruit in well-coated. Pour cherrry mixture into prepared pie crust. Top cherries with bits of butter.
Place second unbaked pie crust on top of cherries, seal, trim, and flute edges. Brush entire crust with beaten egg.
Bake 1 hour and 30 minutes, Cover pie crust loosely with foil if begins to brown excessively. Remove from oven onto to rack to cool. Melt orange marmalade over low heat. Brush warm pie with melted marmalade and cool completely.