Gluten Free Lemon Tart

Lemon Tart
This recipe is based on a combination of sources, but was mainly inspired by Heston Blumenthal’s recent recipe on his recent Channel 4 series.

Despite previous posts where I have been critical of adapting something to be gluten free when the results are never going to match the gluteny equivalent, there are some recipes where it’s worth giving it a go (rather than avoid them entirely).  Gluten Free Lemon tart is one such recipe – zingy lemons, smooth rich filling, biscuity pastry - yes please. It looks like a fiddly affair, but it’s reasonably simple and can be done in stages (e.g. make casing first).  If you’ve got access to a pre-made gluten free shortcrust pastry (e.g. Genius) I’d definitely give that a go.

Ingredients

Sweet Shortcrust Pastry
250g gluten free flour (e.g. my gluten free flour blend here)
150g butter (at room temperature)
50g icing sugar
1 egg yolk
1 vanilla pod
1/2 tsp salt
zest of half a lemon

Filling
Zest (fine grated) and juice of 5 lemons
300ml double cream
390g caster sugar
9 large eggs
1 large egg yolk

Sweet Shortcrust Pastry

  1. Combine the flour and butter in a mixer using a paddle attachment. It will not resemble breadcrumbs as you might expect, but will form a paste.
  2. Gradually add the icing sugar until combined.
  3. In a separate bowl, mix the egg yolk with the vanilla pod and salt.
  4. Add to the mixture gradually and mix until combined.
  5. Shape the dough into a ball, wrap with clingfilm and leave for 30 minutes at room temperature.
  6. Preheat the oven to 190ºC (170ºC fan / gas mark 5)
  7. Roll out the dough between two pieces of baking parchment until the thickness of 2 stacked 2 pence coins.
  8. Line a 26cm tart tin with the pastry – this is where it gets tricky.  First, the best way is to place the tin upside down over the pastry (with baking parchment still on the underside of the pastry only), then try to flip the tin and pastry over at the same time, slipping your hand under the baking parchment as you flip.
  9. Things aren’t going to go to plan – the pastry will most likely tear in several places (what did you expect – it’s gluten free pastry…).  But not to worry – push the pastry  into the corners of the tin, trying to keep the same thickness throughout.  Repair any tears with excess pastry.  Cut the excess pastry away (put some aside to use later) and try to generally tidy up the edges.
  10. Take a sheet of baking parchment and scrunch and unscrunch it several times to remove the sharp edges. Prick the dough all over with a fork, then line the tin with the baking parchment and baking beans (or 1 penny coins) 1/4 of the way up the tin.
  11. Bake for 20-40 minutes.  Vague I know, but you’re looking for no remaining moisture and a light browning, it can take a while.
  12. Meanwhile, mix some of the excess raw dough with an egg (use a hand blender to get it properly mixed).
  13. When the dough looks cooked, remove from the oven and brush with the dough-egg mixture all over, paying attention to the cracks. Return to the oven for 10-20 minutes to cook thoroughly through.
  14. Remove from the oven, or alternatively just turn the oven down to 120ºC and make the filling (you really can’t over bake this pastry).

Filling

  1. When you’re ready to make the filling, preheat the oven to 120ºC and put the tart in to warm up.
  2. Mix all the filling ingredients together in a glass or ceramic bowl.
  3. Place the bowl over a saucepan of simmering water and continue to stir as the mixture warms up – if you have a probe thermometer, you need to get it to 60ºC, if not, this is about as hot as water than comes out of your hot tap, so you can only keep your finger in the mixture for a couple of seconds at most.  This can take a while – as unhelpful as this sounds, if the mixture starts to thicken you’ve reached about 70ºC, which is too far. So hot, but not thickening.
  4. Once the mixture is warm enough, strain the mixture through a fine sieve into a jug.
  5. Skim all the bubbles from the top – and I mean all, even the fine ones, as otherwise they will come back to haunt you.  It’s fine if you leave them, you’ll just have a kind of swirly marbling on the top of the tart. You should have plenty of mixture, so you can afford to lose a fair amount in the skimming.
  6. Slide the oven rack with the tart on it out a little (keeping it flat), and fill the pie up as high as you can. Slide back into the oven and cook for around 20-30 minutes.  You are looking for the filling to warm up to 70ºC all the way through, the centre will be the last part to warm up. BUT - don’t go poking it with the probe thermometer every 5 minutes, you’ll make a mess (more about this later). Just give the tart a shake every so often – if it still looks liquid in the centre, cook it longer, then when it looks firmer test it with the probe.
  7. When cooked, allow the pie to cool at room temperature. Dust each slice with icing sugar to serve, with a spring of mint if it takes your fancy.

Tips and Confessions

- I’ve no idea if you really need to leave the pastry to rest 30 minutes – many people claim it doesn’t matter, it’s more relevant to gluten flour.

- The original filling recipes gives ‘half a vanilla pod’, but I used a whole one, what are you supposed to do with the other half??  Admittedly it was a little bit heavy on the vanilla in the pastry, so you could use a few drops of good vanilla essence instead.

- Getting the pastry into the tin really can be a messy affair – don’t worry, just squidge it in, and try to get it as even as you can.

- If the filling does start to thicken in the bowl over the saucepan, just go ahead and poor it in.  I made two little lemony creme brulee with the left over custard that I warmed until thick, they came out pretty much the same consistency as the tart.

- As I’m sure you’d suspect, I didn’t skim all of those bubbles, and yes, I got swirly marbling. 

- Again, as you’d suspect, I prodded the poor thing with a thermometer every 2 minutes, and it made a mess – it took a while to find a section tidy enough to make the slice above. So aim for just two pokes! And despite Heston’s assurances that using a thermometer was much easier than the ‘wobble test’, it was actually quite obvious when the filling was starting to set just by shaking the tray.  I may not even use a thermometer next time.

- Putting the tart in the fridge didn’t do it any favours – the top of the filling seemed to get wetter, and icing sugar just soaked into the top.  Serve it at room temperature after cooling if you can. Or maybe cook longer? Who knows.

- This is one of those recipes that is a real learning experience, and would be a lot easier cooking for the second time.  I’ve tried to talk through a lot of the hurdles above, you may discover your own, but overall it’s a very satisfying (and tasty!) recipe to make.