Monday 11 April 2016

Of crusts and crumbs

I first developed this crust when I wanted to try this pie filling, which originally calls for a saltine-cracker crumb crust. Mine doesn’t taste like saltines, of course, but it works great anyway - it’s exactly the right amount of crumbliness and has the right salty-sweet flavor to complement the tart, rich lemon filling. I took the above pie to a gathering of non-GF people and it disappeared pretty fast! Proof that despite being different than the original, this crust does exactly what it’s supposed to. I’ve since used the same crust successfully in layer bar cookies that normally use a graham cracker crust, and most recently in this lighter lemon-lime pie I’m sharing with you now.

But, you may be wondering, why not just use GF crumbs? Well:

First, let’s take a look at why crumb crusts are used in the context of wheat based baking. For one thing, crumbs provide an alternative to both the tougher flaky pie crust or the denser, more solid shortcrust pastry made of wheat flour. The latter types require some liquid to mobilize and develop a little gluten and allow some starch to gelatinize during baking (among other reasons), whereas crumb crusts are made with cookies or crackers that have already taken care of that step, and so can be made with just fat and sugar.

The second thing to consider, though, is far more utilitarian: graham crackers/cookies/etc are convenient - they’re cheap and something most people would already have on hand. When adapting to gluten free, then, this convenience ingredient starts to look less and less convenient! It’s both expensive and time consuming to hunt down GF graham crackers - or worse, make them from scratch - just to turn around and pulverize them into crumbs.

So, when neither of the two main reasons crumbs are used in this recipe apply to GF suddenly makes sense to look for another approach! Because we have such a diverse array of GF ingredients available, it’s possible to make a crust with similar texture and flavor from scratch, in one step, no crumbs needed. I find this approach more elegant and far simpler, on top of being delicious. This particular recipe is just one way to do this, but I like it a lot.

This is a nice uncomplicated formula - just rolled oats (half ground into flour), coconut flour, brown sugar, salt, and melted butter (or equivalent). A crumb crust doesn’t need to hold together on its own beyond the most basic level: there’s no dough to roll out, and after baking it’s attached to a stiff, sliceable filling/topping such as cheesecake or key lime pie - the filling supports itself. As a result, this recipe doesn’t need any added binder - the slight binding ability of the oat flour is enough. Coconut flour is unusual amongst flours, as it’s made from the fibrous pulp that is left after fresh coconut has been pressed for oil or grated for milk. As a result, it’s much better at absorbing both moisture and oil than nut meal, almost like a starchy flour in that regard, yet its texture and properties are unlike any other flour. A crust made with starchy flour would be more of a shortbread texture, while coconut flour instead contributes a pleasant crumbliness and unique mouthfeel along with a nice toasty taste (surprisingly enough, the flavor is not particularly coconut-y).
Press and bake the crust...

Lemon-Lime Pie

120 g (heaping cup) rolled oats, divided (see note below)
45 g coconut flour
36 g (3 T) brown sugar
½ tsp salt (or less, to taste)
65 g butter, melted (see note below)

Put half of the oats into a food processor or blender and grind into flour. Combine remaining oat flakes, oat flour, coconut flour, sugar, and salt in a bowl. Stir in melted butter - mixture will still seem dry and floury, but will cling together a bit. Press the mixture evenly into a 9” round glass pie plate, making sure to come up the sides to contain the filling. Put the plate in the fridge to chill about 15 minutes, then bake 15 minutes at 350º F and let cool.

Meanwhile, make the filling:

250 g coconut milk (the kind in a can, not the thin drink)
150 g sugar
2 eggs, separated
60 g (¼ c) lemon juice
60 g (¼ c) lime juice
15 g arrowroot starch

...and it will hold together nicely once the filling has set.
Put the egg whites in the bowl of a mixer fitted with paddle attachment. Put egg yolks in a small dish. Combine coconut milk, sugar, and starch in a small saucepan over low heat, stirring frequently with a silicone spatula, until smooth - it will start to feel slick/slippery when you run the spatula along the bottom of the pan. Carefully whisk some of the warm liquid into the egg yolks, then add that mixture back to the pan (this prevents the yolks from curdling) and continue stirring over low heat until it thickens to the consistency of a thin custard. Remove from heat. Gradually stir in the lemon and lime juice, then turn the mixer on at low speed and with mixer running, slowly pour the whole mixture into the egg whites and mix until smooth.

Pour the filling into the cooled pie crust (it’s OK if it’s not totally cold) and bake the pie until filling is no longer liquidy, about 25-30 minutes.

Chill pie in fridge several hours before cutting. Serve with coconut cream or whipped cream, if desired.

Recipe notes:
  1. I personally like the textural contrast of the oat flakes, but if you don’t want such obvious bits in your crust, you could replace the rolled oat flakes with instant oats, or possibly even just grind them all into oat flour. I haven’t tried an oat-free variation yet - if you do, please let me know how it turns out!
  2. I imagine coconut oil would probably work just fine instead of butter. That said, keep in mind the fact that butter contains a little water (around 14%), while coconut oil is pure fat. I’m not sure whether that little bit makes a difference in this particular recipe, but to be on the safe side, if using coconut oil you might want to sprinkle in about a teaspoon of water. Any dairy-free butter equivalent should work as written.

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