Melt butter in sauce pan on medium heat. Saute onions in butter until translucent. Add flour and salt and reduce heat to low, stirring constantly until sauce is thick and creamy. Add potatoes, carrots, celery, peas, corn and cubed chicken to sauce. Simmer for 10 minutes, stirring constantly. Stir in half and half and continue to simmer for 2-3 more minutes. Add pepper and set aside.
For the crust mix together flour, salt, and baking soda in a large mixing bowl. Add fresh thyme and rosemary. Cut cold butter into mixture piece by piece until the mixture separates into smaller crumbs. Slowly mix cold water and vegetable shortening in, until the mixture becomes one cohesive ball. Wrap in plastic and keep chilled.
When filling is ready, roll out the dough and line four containers with the pasty dough, reserving some dough for the top of the pie. Cover with the top crust, seal the edges, and cut slits in the top to allow the steam to escape. Bake until the pastry is golden brown and the filling is bubbly.