Why did my pastry case crack and leak the filling?

Almost every leak starts as a crack in the blind-baked shell, and almost every crack starts as a thin spot, a stretched patch or a corner that was never properly supported during lining. The filling then finds it, runs underneath, and welds the case to the tin. The good news is that the repair is easy and reliable if you inspect the case before you fill it — which is a step most people skip.

What you'll need

• A loose-bottomed tart tin
• Baking beans or rice
• An egg for sealing
• Reserved raw pastry offcuts

Step by step

1. Keep some raw pastry back before you bake.A walnut-sized piece wrapped in the fridge. You cannot patch a blind-baked case without it and you will not want to make more pastry at that moment.
2. Line the tin without stretching the pastry.Ease it in, do not pull it. Stretched pastry shrinks back during baking, thins at the corner where the base meets the side, and cracks there. Press it gently into the angle with a small ball of pastry rather than a fingertip.
3. Roll thicker than feels necessary.Around 3mm. Very thin pastry looks elegant and cracks under a wet filling. Thin patches are where leaks start.
4. Blind bake with proper support and enough weight.Parchment or foil right into the corners and filled to the top with beans, not a shallow layer in the middle. Unsupported sides slump and crack. See `fix-a-soggy-pastry-base`.
5. Inspect the empty case against the light.Lift the tin and look through the base from underneath, or hold it up to a window. Hairline cracks are visible and this is the moment to deal with them.
6. Patch, then seal.Press raw pastry into any visible crack or hole and smooth it flush. Then brush the whole inside with beaten egg white — or yolk for a richer seal — and return it to the oven for two to three minutes until the egg is set and matte. That film is what actually stops the leak.
7. Fill it in the oven if the filling is very liquid.Slide the case out on its shelf, pour the custard in there, and slide it back. Carrying a full liquid tart across the kitchen is how the last crack appears.

Tips

• Egg white gives a clear, flavourless seal and is the better choice under a pale filling. Yolk gives a stronger seal and a golden colour that suits savoury tarts.
• A loose-bottomed tin makes leaks worse because the seam is a ready-made escape route. It is still worth using — just seal properly and stand it on a tray.
• Standing the tart tin on a preheated baking sheet sets the base fast and reduces both cracking and sogginess in one step.
• For a quiche or a very wet fruit filling, a thin scatter of semolina, ground almonds or fine breadcrumbs on the sealed base absorbs the first of the moisture.

Common mistakes

• Trimming the overhang before blind baking — Pastry shrinks. Trimming afterwards with a sharp knife along the rim gives a clean edge and means a slumped side does not become a short one.
• Filling a case you have not looked at — Thirty seconds of inspection and two minutes of egg wash saves the whole tart. It is the cheapest insurance in baking.

If it doesn't work