I attempted this dessert for the first time when a neighbor dropped off half a bag of key limes as they were headed out of town for an extended trip. (Are key limes used for anything besides making pie?) She kindly lent us her lime squeezer as well, so we were all set. I turned to the web to research the 'best key lime pie recipe' and discovered something shocking - they are all almost identical. Which, when you consider the chemistry involved, isn't that shocking. Though, I confess the first all-nighter I ever pulled in college was trying to make sense of results from a chemistry lab experiment, so admittedly it's not my strong suit.
Back to how simple this is. First, give your 6 year-old a bag of key limes and have him zest the skins (with repeated instructions to 'stop when you see white.') He'll skin a knuckle and ask for a band aid. After he skins a second knuckle you'll probably have enough zest and can let him stop.
Then, after halving the limes, let him use the squeezer to get a measured amount of juice. Yes, there will be a lot on the table and down his arms. Luckily, one bag of key limes contains more than twice as many are needed.
Let him slowly stir as the filling ingredients are combined, and explain how the acid from the limes is reacting with the sugars in the condensed milk, and he'll be able to feel it thickening up. Tell him about your chemistry all-nighter in college. At age 6, the thought of staying up all night sounds unbelievably cool, and not the least bit painful.
While it sets up, give him a bag of graham crackers and a meat tenderizer. So far, I've still always had to transfer it back to the food processor to get fine enough crumbs for the crust, but the kid definitely gives it a good head start.
I don't bother with a topping, though either meringue (you'll have egg whites left over) or fresh whipped cream are encouraged. And, if you want to get fancy, you can sugar some thin slices of key lime for garnish.
Key Lime Pie
Adapted from America's Test Kitchen, and numerous other sources
Several teaspoons of key lime zest
1/2 Cup freshly squeezed juice from key limes
1 can sweetened condensed milk
3 or 4 egg yolks (we get farm eggs, so sizes are inconsistent, and so were the recipes found on the web anyhow)
1 Cup graham cracker crumbs
4 Tablespoons melted butter, cooled a bit
3 Tablespoons sugar
- Zest the key limes, then halve and squeeze enough to yield 1/2 Cup of juice.
- Whisk the zest with egg yolks for a couple of minutes until light. Add the sweetened condensed milk, and then the key lime juice. Mix until combined, you'll feel it thickening immediately, then set aside for 30 minutes.
- In the meantime, pound graham crackers, or skip this and put them in the food processor. Any box of graham crackers will have a recipe on the back to tell you how many of their whole crackers should be used to make a graham cracker crust. Feel free to follow their guidelines instead of these proportions. Some recipes call for maple syrup, but I like the crunch of sugar for this. Add the sugar, drizzle in the melted butter and pulse to combine.
- Press the crumbs onto the bottoms and up the sides of a 9" pie plate, and put the empty crust in a 325 oven for ~15 minutes, which should be exactly how much time you have left to wait on the filling.
- Remove crust from the oven (let cool a bit if you have time remaining) then pour in filling and cook for an additional 15 minutes.
- Let cool on a wire rack and then refrigerate for several hours, or overnight. It's fine to keep it covered or uncovered.