Preheat your oven to 400°F.
Melt the butter in a medium saucepan over medium-low heat. Add the chopped onion and sauté, stirring occasionally, until softened (about 5 minutes).
Stir in the minced garlic, curry powder, and salt, cooking for 1 minute until fragrant.
Add the cauliflower, peas, and carrots. Sprinkle the flour over the vegetables and stir to coat evenly.
Reserve 1 tablespoon of the heavy cream, then gradually stir in the remaining cream along with the chicken broth and cooked chicken. Cook, stirring often, until the filling thickens (about 3-5 minutes).
Transfer the mixture to a 9-inch deep-dish pie pan and let it cool in the refrigerator for about 10 minutes, stirring occasionally.
Spread the filling evenly in the pie pan. Lay the pie crust over the top, folding the edges under to fit the pan neatly. Crimp the edges with a fork for a decorative touch.
Use a sharp knife to make a few small slits in the crust to allow steam to escape. Brush the reserved tablespoon of cream over the crust to encourage browning.
Bake the potpie in your preheated oven for 30-35 minutes, or until the crust is golden brown and the filling is bubbling.
Let the potpie rest for 10 minutes before slicing and serving.