Tartine Lemon Cream

I’ve been using this lemon cream to fill tarts and cakes, most often, coconut cake, but frankly, I’d eat it with a ladle and be very happy. I suspect the lemon cream pushed coconut cake to victory over German chocolate in a room full of avowed chocolate lovers.

The ingredients are simple and few, and the technique is simple, but you must avoid one thing—aluminum. The acid in lemons reacts badly when it comes into contact with aluminum. You can use lined aluminum, but frankly, I’m never letting metal come into contact with my lemon cream ever again. Not after last weekend’s fiasco.

Now, those simple and few ingredients:

For those of you keeping score at home, that is 2 sticks of butter, 3/4 c. sugar, 3 eggs + 1 egg yolk, and 1/2 c. + 2 TBS lemon juice.

You mix everything but the butter together in a non-reactive, heat-safe bowl, then set it over a pot of simmering water and keep stirring until it gets custard-y.

A quirky ingredient fact. You have to get the mixture over heat and keep stirring once you mix the eggs and sugar, because if you let the mixture sit, the sugar cooks the eggs. (Now, I realize the heat is cooking the eggs, too, but trust me, the process is different. I would explain that to you, but this site does a much better job.) So, avoid those hard clumps of eggy protein and just keep stirring.

What is custardy temperature, you ask? Well, I keep that water at something right above a simmer, call it a low, rolling boil, and I cook (while stirring) for 12 to 14 minutes.

When you start, you’ll have something that looks very electric, like this:

When you get to custard stage, you’ll have passed through foamy, and gotten to a paler yellow that sticks to the stirring implement:

You’ll feel more resistance when you stir once you hit the proper point. The mixture will be less liquid and more pudding-like.

At that point, take it off the heat and let it cool a bit, stirring every couple of minutes, for about 10 minutes.

Then, you add in the butter, piece by piece, while whirling it around in the blender. You can use an hand-blender, if you have one, and I will envy you. This is what it looks like before you add the butter:

And this is what it looks like after:

Yum.

While the taste is nothing alike, the change in texture with the lemon cream before & after cooking, then again before & after adding butter, is much like what you see when you make a vinaigrette. Emulsion is the word of the day. You go from a mixture of a couple of ingredients to a richer, thicker, binding of those ingredients.

Once you taste this, emulsion will become one of the most beautiful words you’ve ever heard. Trust me.

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