Preheat oven to 350. Prepare filling. Heat 1 tbsp butter and 1 tbsp canola oil in a large skillet over medium. When the butter is melted add mushrooms, onions, carrots and asparagus. Depending how large your skillet is you may need to do 2 batches. Cook veggies until nearly tender, then remove from heat and set aside. Add diced chicken to the veggies, stirring gently to combine.
Prepare crust. In a large bowl, combine flour and salt. Use a pastry blender to cut in the butter until large crumbs form. Set aside. In a small bowl, beat together the egg, water, vinegar and molasses. Add liquid to flour mixture, stirring just until dough forms. It may be necessary to use your hands to make a smooth dough. Try not to handle it too much or it becomes tough. Divide the dough into two portions. Roll each into a circle between waxed paper. Use one to line a round casserole dish, then bake about 10 minutes. Set the other circle of crust aside for now.
Prepare sauce. In a small pot, combine water, mushroom bouillon and pepper. Heat to nearly boiling. In a small bowl or glass Pyrex style measuring cup combine flour with enough milk to equal about 1 cup total. Stir thoroughly until smooth. Slowly pour into hot bouillon, stirring constantly. Add parmesan. Cook and stir until the mixture thickens. Remove from heat and set aside.
Build the pot pie. Transfer the chicken and veggie mixture to the prepared crust. Pour over about 1 cup of the sauce. Top with remaining circle of crust, tucking under edges like for pie. Put at least one slit in the top of the crust to vent. It’s best to bake it on top of a cookie sheet just in case it drips, it’s a bit of guesswork how much sauce to add for which casserole dish you’re using.
Bake at 350 for about an hour, until crust is golden. Let cool a few minutes before serving – the crust will become more crisp as it begins to cool. Slice, serve and enjoy!