lemon bars and curd/custard/crme pat confusion
What I’m reading: Why is Food Education so Unappetising? by Thea Everett, for Vittles magazine. A really interesting narrative about food education over the past century
What I’m listening to: Blindboy’s mental health plan for the New Year. Helpful and educational but also light-hearted
What I’m eating: fish and chips at Auckland Fish Market (below)
This week, I really wanted to make lemon bars. I wanted a shortbread-y base, and a topping that was less “curd”-like and more “custard”-like - as in, smooth like the baked custard in a tart rather than rich like a baked curd.
A shortbread base is fairly standard for bars like these, but I went for a slightly different approach in the mixing method. As I discussed a few weeks ago with my two Christmas shortbread recipes, there are usually two schools of thought when it comes to shortbread: the “breadcrumb” method, which involves rubbing the butter into the dry ingredients (either by hand or using a food processor), and the “creaming” method, which involves creaming soft butter with sugar, before mixing in the dry ingredients. Although this is definitely a shortbread-style base, I wanted it to be a bit more robust, and therefore not quite as crumbly as shortbread often is. So I’ve opted for similar proportions in terms of butter:sugar:flour, but I’ve melted the butter instead, which produces a softer dough that is much easier to press into the tin - and easier to cut neatly, provided your knife is nice and sharp.
The filling, however, is what sent me into a tailspin. I researched a few lemon bar recipes, and found a whole range of options, from curd to custard to crème pat. This was deeply unsettling, as although the ingredients for these fillings are quite similar, they are all completely different textures. Here’s a quick breakdown of the options:
Lemon curd:
Lemon curd (or any curd, for that matter) is usually made from fruit (in this case, lemon zest and juice), eggs (and/or yolks), sugar and butter. These ingredients are whisked together over a medium heat until the curd has thickened. Some people use a mixing method similar to a hollandaise, where you whisk or “mount” the butter into the cooked curd, which I find produces a silkier result. Either way, it’s a pretty magical thing to make, as it thickens like a crème pat and sets fairly firmly without the use of starch like flour or cornflour.
Crème patissière:
Crème pat or pastry cream is a set custard made of eggs (or yolks), milk (or cream), sugar and starch (usually flour or cornflour). Again, there are a few ways of making it, but a common way is to heat the milk (or cream) to near boiling, then stream this into whisked eggs, sugar and flour, before returning to the pan and whisking over a medium heat until it has thickened. Once set, it’s quite stable and can be piped or used to fill blind-baked tart shells - or folded into whipped cream to make crème diplomate etc. You can make a crème pat lemon flavoured by adding lemon zest and/or juice - though I would recommend adding them to the egg/sugar/starch mixture, or you risk curdling the milk.
Custard:
This is a catch-all term for egg-based fillings, most of which are not cooked before filling the tart. A good example is this famous Marcus Wareing recipe. Here, the cream is boiled before being added to the egg yolks and sugar - but this is mainly to dissolve the sugar and ensure that everything is nice and homogenous, and it’s not technically a “cooked” custard (until it’s baked in the tart shell).
Now this is all well and good, but I still couldn’t quite get a handle on what type of filling was going to produce the result I was after. This recipe, for example, (and this one) calls the filling “curd”, but it is not cooked before being poured onto the base. Can it still be called a curd if it’s baked in the base, but not before? This recipe, by Claire Saffitz, also calls the filling a curd, but this time it’s cooked before being poured onto the base - but this curd uses cornflour as a stabiliser, which is FINE (and actually really smart) but does that make it a crème pat instead of a curd? Meanwhile, recipes for custard tarts that had a very similar texture to what I wanted to achieve like this one and this one had absolutely no starch for stabilising, and instead relied on the eggs to set the custard! Absolute mayhem.
I’m afraid I have no answers for you here - I just wanted to bring you down my lemon bar rabbit hole. Now that you’re here, I’m delighted to share that I decided to embrace the chaos for my lemon bar filling, and make a HYBRID filling that is part curd, part custard and part crème pat. Or maybe it’s none of those things. It’s essentially a cream-based (custard), part-cooked (crème pat) lemony (curd) filling that I can confirm DOES bake beautifully and sets nicely, and is lemony and also silky smooth.
I would also like to note that if I had in my possession a blowtorch, I would have gone TO TOWN and bruléed the heck out of the top of this after it was baked. I don’t, though, so I garnished with candied lemon slices and some mint. If you have a blowtorch, though, brulée away x
Base
120g butter, melted
220g flour
40g icing sugar
1 tsp salt
Zest of 2 lemons
Filling
130g cream
4 eggs
110g caster sugar
Zest and juice of 2 lemons (you want about 80g lemon juice)
1 tsp salt
5g cornflour
Candied lemon slices
120g sugar
100g water
1-2 lemons
Method
Preheat the oven to 180C. Line a 9”/20cm square tin with baking paper.
For the base, place the flour, icing sugar, salt and lemon zest in a bowl, then add the melted butter and mix to combine. Press this mixture into the prepared tin, and bake in the preheated oven for 18-22 minutes, until golden brown. Allow to cool slightly before adding the filling.
Decrease the oven temperature to 160C.
Place the cream in a saucepan and place over a medium heat until it has just started steaming.
Place the eggs, sugar, zest, juice, salt and cornflour in a bowl, and whisk to combine. When the cream starts steaming, pour over this mixture, whisking all the time. Pour this mixture back into the saucepan, and heat over a medium heat, whisking constantly, for about 4-5 minutes, until it is thick enough to coat the back of a spoon, and is steaming. It should be about 60C.
Pour the mixture over the base, and tap gently against your countertop to expel any bubbles.
Place back in the oven for 12-14 minutes, until just about set, with a very slight wobble in the centre. Allow to cool at room temperature for 30 minutes, and then allow to set fully in the fridge for at least 2 hours.
Use a hot, sharp knife to cut.
For the candied lemon, place the water and sugar in a saucepan over a medium heat and bring to a boil, stirring occasionally to ensure the sugar dissolves. Use a sharp knife or a mandoline to cut the lemon into thin slices. Place in the boiling syrup, and reduce to a simmer. Use a cartouche (circle of baking paper) to cover the surface, and cook gently until the lemon slices have turned translucent - about 15 minutes. Remove carefully from the syrup and allow to cool on greaseproof paper before using.
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