In 3 litre saucepan over medium heat, melt buttter. Add onion, cook, stirring often until tender. Combine flour, bouillon, thyme and pepper and stir into onion mixture. Cook, stirring often, 1 minute. Stir in milk gradually; cook and stir until mixture thickens. Remove from heat and stir in potatoes, chicken, vegetables and parsley. Spoon hot filling into prepared crust. Cover with top crust, seal edges and cut slits into top crust to allow steam to escape during baking. Bake at 375 degrees 45 minutes to 1 hour, or until filling begins to bubble and crust edges are brown.