Golden Potato-Onion Cheese Tart

Ingredients

• 1 chilled savory herb pastry shell, fitted into a 9-inch tart tin or small rectangular tray
• 650 g waxy or all-purpose potatoes, peeled if preferred, sliced 2-3 mm thick
• 2 medium onions, thinly sliced
• 1 tablespoon butter
• 1 tablespoon olive oil
• 1 teaspoon fresh thyme leaves, plus extra to finish
• 160 g sharp cheddar, grated
• 2 large eggs
• 160 ml cream, half-and-half, or whole milk
• 1 tablespoon chopped chives
• 1/2 teaspoon fine salt, plus more for potato water
• 1/2 teaspoon black pepper
• Optional: 1 teaspoon Dijon mustard in the custard for extra savory depth

Method

1. Heat the oven to 190C / 375F. Chill the lined tart shell while the filling is prepared. If the pastry is soft, blind bake it for 10 minutes with baking weights, then remove the weights and bake 4 minutes more.
2. Cook the onions in butter and olive oil over medium-low heat for 12-15 minutes, stirring often, until soft, golden, and sweet. Add thyme in the final minute. Do not rush this step; pale raw onion will taste sharp in the finished tart.
3. Parboil the sliced potatoes in salted simmering water for 4 minutes, just until flexible but not falling apart. Drain carefully and let them steam-dry on a tray for 5 minutes.
4. Layer half the potatoes in the tart shell, overlapping slightly. Scatter over half the onions and half the cheddar. Repeat with the remaining potatoes, onions, and cheddar.
5. Whisk eggs, cream, chives, salt, pepper, and optional Dijon. Pour slowly around the tart so the custard settles between the layers without flooding the top.
6. Bake 35-45 minutes, depending on tin shape, until the pastry is crisp, the cheese is bubbling, and a small knife inserted in the center meets tender potatoes.
7. Rest 10 minutes before slicing. Finish with thyme, chives, and a little black pepper. Serve warm or room temperature with salad, pickles, roasted tomatoes, or a simple herb yogurt.

Tips

• Cook onions up to 3 days ahead and refrigerate.
• Slice and parboil potatoes the day of baking for the best texture.
• Bake the tart up to 1 day ahead, cool, cover, and refrigerate. Reheat at 170C / 340F until warm and crisp at the edge.
• Leftover slices keep 3 days chilled. Reheat on a tray rather than in a microwave if you want the crust to stay crisp.