Mashed Potato Casserole Recipe

Ingredients

• 907 g (2 lb; 3–4 medium)sweet potatoes, peeled and cut into small cubes
• 907 g (2 lb; 4–5 medium)Yukon gold potatoes, peeled and cut into small cubes
• To tastekosher salt
• 180 ml (¾ cup)whole milk
• 180 ml (¾ cup)double cream
• 113 g (1 stick; 4 oz)butter, melted and cooled
• To tastefreshly cracked black pepper
• 16 g (2 tablespoons)plain flour
• 1leek, white and pale green parts only, cut into 6 mm rings, rinsed well and patted dry
• 30–45 ml (2–3 tablespoons)avocado oil
• 6 slicesbacon or turkey bacon, cooked; omit for a vegetarian version

Instructions

1. 1

   Boil the potatoes

   Put the sweet potatoes and Yukon gold potatoes in separate saucepans. Cover each with water by 2.5 cm, salt generously and bring to the boil. Cook until fork-tender, then drain and return each type to its pan.

2. 2

   Mash the potatoes

   Heat the oven to 220°C (425°F). Whisk the milk, cream and butter together in a bowl, then divide the mixture between the two pans. Mash each batch with a potato masher or hand blender until smooth, and season with salt and pepper.

3. 3

   Prepare the dish

   Lightly coat a casserole dish with cooking spray. Use an oval dish or a rectangular dish measuring about 23 × 28 cm (9 × 11 inches).

4. 4

   Layer the potatoes

   Spread the mashed sweet potatoes in the prepared dish and smooth them into an even layer with the back of a spoon or a spatula. Add the mashed Yukon gold potatoes on top and spread them to the edges, making small dips and crevices in the surface.

5. 5

   Bake until golden

   Bake for 20–25 minutes, until the top is golden.

6. 6

   Fry the leeks

   Meanwhile, toss the leeks with the flour and a pinch of salt to coat. Heat the avocado oil in a medium saucepan over medium-high heat for 2 minutes. Add the leeks and fry, turning occasionally, until crisp and golden around the edges. Transfer them to a plate lined with kitchen paper.

7. 7

   Finish and serve

   Season the crispy leeks with more salt and pepper, then scatter them over the casserole. Serve immediately.

What is mashed potato casserole?

A mashed potato casserole is a baked dish of prepared potatoes, finished in the oven rather than served straight from the pan. This American-style version layers sweet potato mash with Yukon gold mash for a contrast in colour and flavour.

Separate pans let each potato cook and mash on its own before the layers are assembled. Cream, milk and butter make both layers smooth, while the oven browns the textured top.

Nutrition and macros by portion

The nutrition label shows one serving as written: 301 calories, 5g protein, 34g carbs, 17g fat.

Most of the carbohydrates come from the sweet potatoes and Yukon gold potatoes. Butter, cream, milk and avocado oil contribute much of the fat, while the potatoes and bacon provide some protein. Pair a serving with green vegetables or a salad for a more balanced plate.

Why use two kinds of potato?

Sweet potatoes: Their mash brings a naturally sweet note and forms the base layer. Cut the cubes to a similar size so they cook evenly.

Yukon gold potatoes: These make the upper layer and balance the sweetness with a more savoury potato flavour. Keeping the varieties separate preserves the casserole’s distinct layers.

Getting smooth mash

Fork-tender potatoes: Cook each variety until a fork slips into the cubes easily, then drain them well. Excess water can leave the mash loose.

Dairy mixture: Whisk the milk, cream and melted butter before dividing it between the pans. Mash until smooth and season each batch to taste.

Layering and browning

Even layers: Spread the sweet potato mash first, then smooth the Yukon gold layer right to the edges. This keeps the two colours visible when serving.

Textured top: Small dips and crevices in the upper layer give the surface variation as it bakes. Look for a golden top after 20–25 minutes.

Crisp leek topping

Dry leeks: Rinse the sliced leek well to remove any grit, then pat it dry before coating it with flour. Dry pieces are less likely to splutter when added to the hot oil.

Fry in batches if needed so the pieces have room to crisp. Lift them onto kitchen paper, then season and add them just before serving to preserve their crunch.

Make-ahead and serving

The mashed potato layers can be assembled ahead, making this dish useful for a planned meal. The topping is best fried close to serving time so it stays crisp.

Serve the casserole alongside a green salad or cooked vegetables for freshness. If using bacon, scatter the cooked slices over the top with the leeks or serve them alongside.

Recipe notes & tips

• Use separate pans so the two potato varieties can be mashed into distinct layers.
• Cut the potato cubes to a similar size to help them cook at the same rate.
• Drain the potatoes thoroughly before returning them to their pans.
• Pat the leek rings dry after rinsing them to reduce splattering in the oil.
• Add the fried leeks just before serving to keep them crisp.

Variations

• Vegetarian version: Omit the bacon as directed and finish with the fried leeks.
• Turkey bacon: Use cooked turkey bacon in place of the bacon.
• Extra pepper: Add more freshly cracked black pepper to the mash or leek topping.
• Make ahead: Assemble the potato layers in advance and bake when ready to serve.
• More leeks: Fry additional leek rings if you want a more generous crisp topping.

Common mistakes to avoid

• Mixing the potatoes together: Mash each variety separately to keep the layers distinct.
• Undercooking the cubes: Boil until fork-tender so the mash can be made smooth.
• Watery mash: Drain the potatoes well before adding the milk, cream and butter.
• Wet leeks: Pat the rings dry after rinsing to limit splattering in the hot oil.
• Crowding the leeks: Fry in batches if needed so they can crisp rather than steam.

How to store

Refrigerate leftover casserole in a covered container for up to 3 days. Reheat in an oven until hot throughout; the leek topping may lose its crispness, so add freshly fried leeks if desired.

Frequently asked questions