First, boil the potatoes. Scrub the potatoes to remove any dirt, and place them in a pot filled with water. Once the water boils, cook the potatoes until fork tender or for 20 minutes.
In the meantime, thinly slice your onion into half moons.
Heat olive oil in a small saucepot and add onions. Cook the onions for 10 minutes or until soft. Season the onions to taste with salt and cook until caramelised, on low heat for 20 minutes.
Add thyme to the onions in the last few minutes of cooking.
Drain the boiled potatoes and leave them in the colander for 2 to 3 minutes to steam dry, so the mash isn't watery. Once they are cool enough to handle, peel the potatoes and place them into a bowl. Add butter and cream cheese. Mash the potatoes until almost smooth. If needed, add a splash of milk.
Stir in 1 cup cheddar cheese and mustard.
Stir through the caramelised onions. Preheat the oven to 200°C (180°C fan, Gas 6).
Transfer the potatoes to a baking or pie dish. Run a fork over the top to make ridges, then top with the remaining cheese. Bake the potato pie for 20 minutes, until golden and crisp on top. Serve the potato pie with some fresh salad or steamed peas on the side.
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 the microwave or oven.To Freeze: Freeze in an airtight container for up to three months. Defrost in the fridge and reheat in the microwave or oven. To freeze in portions, bake the mixture in individual ramekins, let them cool, then cover and freeze. Reheat from frozen at 180°C fan for 30 to 35 minutes, until piping hot all the way through.Tip 1: If you want this to be more like a Shepherd's pie, you can add layers of tomato sauce and beef.Tip 2: Scoop servings into muffin tins for mini potato pies!Tip 3: You can add beef, sausages, pork, or chicken into this recipe if you aren’t vegan or vegetarian. If you are vegan/vegetarian you could add tofu if you wished.