Silky, cheesy layers of tender potato baked until bubbling and golden, with a cream sauce that soaks into every slice.
Step 1: Prep oven & dish
Preheat oven to **180°C / 350°F (160°C fan)**. Grease a **large baking dish** (about **33 x 23 cm / 13 x 9"**) with butter.
Step 2: Slice potatoes
Slice potatoes into **3 mm / 1/8"** rounds (a mandoline makes this fast and even). Keep slices stacked so they don’t brown; no need to rinse.
Step 3: Make the cream sauce
In a saucepan over **medium heat**, add **butter + oil**. Stir in **garlic** for **30 seconds** until fragrant (don’t let it brown). Pour in **cream + milk**, add **salt, pepper**, and **mustard (if using)**. Heat until **steaming hot** and just starting to bubble at the edges, **3–5 minutes** (don’t boil hard).
Step 4: Layer
Arrange one-third of the potato slices in the dish, overlapping slightly. Ladle over one-third of the hot cream sauce. Sprinkle with **1/2 cup (50 g)** cheese. Repeat **2 more times**, finishing with cheese on top.
Step 5: Bake covered
Cover tightly with foil. Bake **55 minutes**, or until a knife slides through the centre with only light resistance.
Step 6: Bake uncovered to brown
Remove foil and bake **15–20 minutes** more until the top is **deep golden** and the sauce is **bubbling around the edges**.
Step 7: Rest (this matters!)
Rest **10–15 minutes** before serving so the sauce thickens and the layers set.
| Calories | 420 kcal |
| Protein | 12g |
| Carbs | 38g |
| Fat | 24g |