Key lime, by special request

As I gear up to bake the next family birthday cake, I guess it's about time I shared the last one. It was actually a tart if we're being careful with our words—never a bad idea.

"Key lime pie's my favourite," she casually mentioned. "And my birthday's next month," she continued, just in case I wasn't taking the hint. (That was my niece S. back in March, during our brief stint as roomies after we arrived back in Canada.)

I feigned disinterest, but secretly filed this handy piece of information away. Little did she suspect that the lemon meringue tart I brought to Easter dinner was a prelude to the main event. When I tweeted a photo of key lime cream several weeks later, her response was near instant: "You totally just made my day!" Which in turn made mine.

Key Lime Tart
Yields one 20-cm (8-inch) tart + four 8-cm (3-inch) tartlets

Sweet pastry:
300 grams unsalted butter, at room temperature
190 grams icing sugar
60 grams toasted ground almonds
1 teaspoon vanilla
2 eggs
500 grams all-purpose flour
1 teaspoon fleur de sel

Key lime cream:
200 grams sugar
4 large eggs
130 millilitres key lime juice
Zest from half the key limes
300 grams unsalted butter, at room temperature

Italian meringue:
50 grams water
150 grams sugar

2 egg whites
35 grams sugar

Begin by preheating your oven to 350 degrees Fahrenheit. Scatter 60 grams worth of whole almonds onto a rimmed baking sheet and toast for 7-10 minutes, or until fragrant and golden. Transfer the toasted almonds to a plate to cool completely before grinding them to a fine meal in a food processor.

In a medium bowl, cream the butter until soft and smooth. Mix in the icing sugar, ground almonds and vanilla. Add the eggs one at a time, beating well between each addition. Stir in the flour and fleur de sel, mixing just until incorporated. Be careful not to overwork the dough at this point in the game!

Divide the dough into three equal balls. Lightly pat each ball into a disc and wrap it tightly in plastic wrap. Refrigerate overnight (or for up to two days) or freeze for up to a month.

Lightly grease your tart pan. Roll out your sweet pastry into a circle that measures the diameter of your tart pan, plus 5 centimetres. Working quickly, press the dough into the pan. Wrap it tightly in plastic wrap and chill for an hour.

Preheat your oven to 350 degrees Fahrenheit. Take the lined tart out of the refrigerator, remove the plastic wrap and replace it with baking paper. Fill the paper with dried rice, dried beans or baking weights. Bake for 17-25 minutes, remove the weights, and then continue baking for another 3-5 minutes (or until light golden brown). Cool completely before filling.

Meanwhile, prepare the key lime cream. Start by filling your sink with 3-4 centimetres of cold water and bringing a saucepan with several inches of water to a boil. Meanwhile, cut the butter into large chunks and set it aside in a small bowl. In a medium heatproof bowl, combine the sugar and lime zest. Use your fingers to rub the two together until the mixture is moist and aromatic. Whisk in the eggs, followed by the lime juice.

Place the heatproof bowl over the saucepan filled with boiling water to create a double boiler, turning down the heat as needed to maintain a slow but steady simmer. Stir continuously with a wooden spoon until the mixture reaches 185 degrees Fahrenheit. This could take awhile. As soon as you hit 185 degrees Fahrenheit, remove the bowl from the heat and set it in the sink filled with cold water.

Once the temperature has dropped to 140 degrees Fahrenheit, remove the bowl from the sink and whisk in the butter one piece at a time. Once all of the butter has been added, blend the cream for 8 minutes using a stand or handheld mixer or immersion blender. At this point, the mixture can be cooled for immediate use or refrigerated for up to four days. To store the lime cream, scoop it into a bowl and press a piece of (heatproof) plastic wrap onto the surface to create an airtight seal.

Once your baked tart shell and lime cream are sufficiently cool, spread or pipe the lime cream into the tart shell. At this point, refrigerate the tart for at least an hour before getting started on the meringue.

Now let's merengue—er, make meringue. In a small saucepan, heat the water and 150 grams of sugar until it reaches 239 degrees Fahrenheit. Meanwhile, using a stand mixer, beat the egg whites and a pinch of salt on low until foamy. Add the 35 grams of sugar gradually, then increase the mixer speed. Beat the mixture until soft peaks form. Here's the key: you need the simple syrup to reach the right temperature right around the same time that soft peaks are forming in your egg whites. If you're waiting for your simple syrup to catch up, simply lower your mixer speed until the syrup is ready. Ready?

Turn your mixer speed to medium, then pour the boiling syrup into the egg white mixture in a steady stream. Increase the mixer speed to high and beat the mixture until the outside of the mixing bowl is no longer hot (just slightly warm).

Remove the tart from the refrigerator and pipe or spoon the meringue on top. Use a blow torch or your oven's lowest broiler setting to lightly brown the top. Careful here—a few seconds can be the difference between perfectly toasted and definitely burned!

Source: A key lime variation on Fanny's tarte au citron meringuée over at Foodbeam.