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Key lime pie

This recipe is taken from the blog post “Key lime pie and the methods of rationality”; read the post if you want the full story about how the recipe was developed, and much more.




Note: All ingredients are listed in the order in which they’re to be added.


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Flowchart of the process.
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Part I: Prepare the crust

  1. Melt the 5 tbsp butter on low heat; remove from heat and set aside.
  2. In a food processor, process the 11 graham crackers with the 5 tbsp dark brown sugar into fine crumbs.
  3. Add the melted butter to the food processor; process until fully incorporated.
  4. Turn out the crust mixture into a 9″ pie dish. Press the crust into bottom and sides of pie dish.
  5. Place crust in refrigerator to chill for approximately 15 minutes. Set oven to 350°F, to preheat.

Part II: Begin preparing the filling

While the crust is chilling and the oven preheating, start working on the filling:

  1. Zest the limes.
  2. Halve (or quarter) and juice the limes. Make sure you have the right amount of juice (23 cup if using regular lime juice, or 12 cup if using Key lime juice).
  3. Separate the eggs; place the (four extra-large) yolks into medium mixing bowl. (Preserve the whites for another use.)
  4. Open the can of sweetened condensed milk.

Part III: Prebake the crust

  1. Remove crust from refrigerator (where it has now been chilling for about 15 minutes), and put it in the oven. Bake for 10 minutes (or until golden).

Part IV: Mix the filling

While the crust is baking, prepare the filling mixture:

  1. Using the hand mixer with the whisk attachment(s), beat the 4 extra-large egg yolks on high speed until light and thick.
  2. Add the 1 tbsp lime zest to egg yolks, and beat on low speed until incorporate.
  3. Add the 14 oz. sweetened condensed milk and 23 cup lime juice; beat on low speed until just incorporated.

Part V: Fill and bake the pie

  1. Remove the crust from the oven once it’s done prebaking. (At this point, the filling mixture should be done.)
  2. Pour filling mixture into prebaked pie crust.
  3. Put filled pie back in the oven; bake for 10 minutes, or until just set (it should jiggle slightly in the middle, while the edges should be fully set).
  4. Remove pie from oven, and set on rack to cool.

Part VI: Make the topping

Make whipped cream. Use your preferred method, or as follows:

  1. Combine the 2 cups heavy cream, 13 cup white sugar, and 2 tsp vanilla extract in a large bowl.
  2. With electric hand mixer, beat cream on high speed until stiff peaks form.

Part VII: Assemble the pie

  1. Spread whipped cream over the cooled pie.
  2. Garnish with lime zest.

Part VIII: Chill and enjoy!

  1. Chill pie in the fridge for at least 4 hours (preferably overnight).
  2. Eat the pie!

What can go wrong

The Dessert Bible includes a “What Can Go Wrong” section after many of the recipes therein; I have always found these to be tremendously useful.

Fortunately for me (and for anyone reading this and thinking of trying the recipe), certain readers of this blog have already tried their hand at making the pie in accordance with the instructions above. I am given to understand that the results were delicious—but flawed. (Don’t get discouraged, anonymous blog readers! Keep trying! The world is better for your efforts!) Here, then are some things that can go wrong when making a Cognitive Pie™ Key lime pie.

Inadequate egg separation

Perfectly separating yolks from whites is tricky. Making sure no yolk gets into the whites (critical if you’re making meringue, for instance) takes care but is doable; making sure no white gets into the yolks is impossible. Still, it’s very possible to minimize how much egg white ends up in your yolks—and it’s definitely something you want to aim for, in recipes like this.

This is good:

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This is not quite as good:

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What happens if whites get into the yolks? The texture suffers. It’ll be a bit more rubbery and less smooth—not ruinous, but not perfect. To avoid this, take care when separating the eggs. One trick that helps here is to make sure the eggs are cold (i.e., right out of the fridge) when you separate them.

Not beating the egg yolks well enough

This is step #11 in the recipe. You want the yolks to be very thick and pale before you add the other ingredients. (If you try to beat the yolks after you’ve already added the lime juice or sweetened condensed milk, it won’t work.)

If you don’t do this quite well enough, it’s not the end of the world… but the filling will be denser, and not as smooth and “custardy”, as it could be.

Overbeating the filling

Counterintuitive though it might be, given the preceding heading, it’s true: you can overbeat Key lime pie filling. The trick is, after you’ve added the juice, zest, and sweetened condensed milk to the egg yolks—then you want to minimize how much you beat them. Mix just to incorporate fully—no more.

Otherwise, this can happen:

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Yes, the filling bubbles and cracks. You want the filling to be smooth and without any bubbles or cracks when it’s baked. So be gentle with that filling, once you’ve added things to the beaten yolks!