Caramelised Onion, Gruyère and Thyme Quiche

STEP 1: MAKE AND REST THE PASTRY

Rub the cold butter into the flour and salt until the mixture resembles breadcrumbs. Mix in the egg yolk and just enough ice-cold water to bring it into a dough — no more. Flatten into a disc, wrap and chill for at least 30 minutes. Cold, rested pastry holds its shape and browns evenly.

STEP 2: LINE THE TIN AND LEAVE THE PASTRY PROUD

Roll out to about 3mm and line the tin, easing the pastry into the flutes without stretching. Leave the excess overhanging rather than trimming flush — you will trim after baking, which prevents shrink-back and gives a clean edge to fill below. Prick the base, then chill for another 20 minutes.

STEP 3: BLIND BAKE TO REAL COLOUR

Heat the oven to 200°C / 400°F (fan 180°C) with a baking sheet inside. Line the case with parchment and baking beans and bake on the hot sheet for 15 minutes. Remove the beans and parchment, trim the overhang, then bake for a further 10–12 minutes until the base is dry and the rim is deep golden — not pale. This is the central correction: a case baked to colour and fully cooked.

STEP 4: SEAL THE CASE AGAINST DAMPNESS

While the case is still hot, brush the base and sides with the reserved egg white and return it to the oven for 2 minutes to set a thin seal. This waterproofs the pastry so the custard cannot soak in and the base stays crisp. Reduce the oven to 160°C / 325°F.

STEP 5: CARAMELISE THE ONIONS

Melt the butter with the oil over medium-low heat. Add the onions and salt and cook gently, stirring often, for 30–40 minutes until collapsed, jammy and deep gold, adding the pinch of sugar once they soften to help them along. Finish with the optional splash of sherry vinegar and let it cook away, then cool slightly. This slow-built sweetness is the praised flavour — do not rush it.

STEP 6: MIX THE SILKY CUSTARD

Whisk the eggs and yolks with the cream and milk until smooth, then season with the pepper, nutmeg and a light pinch of salt (the Gruyère is salty). Stir in the thyme leaves. The extra yolks and cream-forward ratio give a custard that sets soft and moist rather than baking out dry.

STEP 7: FILL BELOW THE RIM AND BAKE GENTLY

Scatter the caramelised onions and two-thirds of the Gruyère over the baked base. Set the tin on the pulled-out oven shelf, pour in the custard to just below the rim, scatter over the remaining cheese and the thyme sprigs, then slide the shelf in — filling in place avoids spills. Bake at 160°C / 325°F for 25–35 minutes until set at the edges with a faint wobble at the centre. Pulling it while it still trembles is what keeps it from drying.

STEP 8: REST, THEN SERVE

Cool in the tin for at least 20 minutes so the custard finishes setting and slices cleanly. Serve just warm or at room temperature, with the golden edge on show.