Preheat your oven to 190C (375F). Start by preparing your ingredients; cut the chicken breasts into bite-size pieces.
Prepare your onions, by slicing them into thin halfmoons. Peel and thinly slice the garlic cloves.
Heat 1 1⁄2 tbsp olive in a large skillet. Add the chicken and season to taste with salt and pepper. Cook the chicken until golden on all sides. Remove the chicken from the skillet.
In the same skillet, cook onions for 4-5 minutes, stirring. Add garlic and cook until fragrant, for 30 seconds.
Add mushrooms and thyme. Cook, stirring, for 5 minutes or until they release their juices.
Now, whisk vegetable stock with flour. Add the vegetable stock mixture with cream and mustard into the skillet. Simmer for 15-20 minutes or until thickened.
Transfer the mixture into a pie pan. Place the puff pastry sheet over the filling and trim the excess ends. Make a few slits in the puff pastry to release steam. Brush the puff pastry with olive oil and bake the pie for 30-35 minutes. Cool slightly before serving.
Notes
Step-by-Step Photos: My blog post includes helpful step-by-step photos to help guide you through making this recipe.Substitutions & Variations: I have included a list of these in the post above.To Store: Store in an airtight container in the fridge for 2-3 days. Reheat in an oven or the air fryer for best results.To Freeze: Freeze for up to two months in an airtight container. Defrost in the fridge and then reheat.Tip 1: If you want to use puff pastry on both the bottom and the top, be sure to pre-bake the bottom one before adding the filling.Tip 2: If your filling is too runny, add more cream or flour.Tip 3: To avoid burning the edges of your pie, you can wrap them in tin foil until you near the end of the baking time.