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1
Beat the butter in a medium bowl with an electric mixer on medium-high until smooth.
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2
Add the sugar and salt and continue to beat until evenly combined.
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3
Scrape down the sides of the bowl, then beat in the egg yolk.
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4
Add half of the flour, beating until just crumbly.
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5
Scrape down the bowl again; add the remaining flour and then the sour cream or yogurt, beating just until the dough is evenly moistened.
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6
Turn dough onto a lightly floured work surface and knead lightly to bring it together.
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7
Roll the dough between 2 generously floured sheets of waxed or parchment paper into a circle about 1/4-inch thick with a rolling pin.
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8
Refrigerate for 1 hour.
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9
Cut out 6 (4 1/2-inch) rounds using an inverted bowl or round cookie cutter.
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10
Place rounds in the muffin tins and, using a small shot glass or your fingers, press into the corners and about halfway up the sides for a snug fit (see photo).
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11
Freeze dough in the muffin tin for 30 minutes.
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12
Position a rack in the lower third of the oven and preheat to 325 degrees F. Spray the outside of 6 standard muffin liners with cooking spray and place in the crusts.
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13
Fill with dried beans or pie weights.
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14
Bake crusts until just brown around the edges, about 25 to 30 minutes.
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15
Remove from the oven and cool for about 1 minute; then carefully remove the muffin liners and baking beans.
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16
Return pan to the oven and continue to bake until crusts are cooked through and evenly browned (see photo), about 15 to 20 minutes more.
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17
Cool slightly.
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18
Then carefully remove crusts from the muffin tin and cool completely on a rack.
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19
Combine the sugar, cornstarch, and yolks in a nonreactive saucepan.
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20
Whisk constantly over medium-low heat until the mixture is smooth and sugar dissolves, about 1 minute.
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21
Add the lemon and lime juice and zest and continue to cook, whisking constantly, until the mixture is as thick as sour cream and is just about to simmer, 3 to 4 minutes.
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22
(Take care to stir into the sides of the pot so that all curd thickens evenly.)
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23
Strain through a fine mesh strainer into a bowl.
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24
Whisk in the butter a little at a time, until smooth.
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25
Stir occasionally until cooled.
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26
(Setting the bowl in a larger bowl of ice will speed this up.).
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27
Fill each tartlet with 1 1/2 tablespoons of the cool lemon filling.
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28
Bring a few inches of water to a boil in a saucepan that can hold a standing mixer's bowl above the water.
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29
Whisk together the egg whites, sugar, cream of tartar and salt in the bowl by hand.
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30
Set the bowl above the boiling water and continue whisking until the mixture is hot to the touch (135 degrees F) and the sugar dissolves, about 1 to 2 minutes.
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31
Transfer the bowl to the mixer fitted with the whisk attachment and beat the whites at medium-high speed until they hold soft peaks.
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32
Increase speed to high and continue to beat to make a stiff, cool meringue, about 10 minutes.
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33
Dollop or pipe on top of the filling.
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34
Just before serving, preheat the broiler to high.
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35
Set the pies on a baking sheet, and place under the broiler until the meringue is evenly toasted, about 2 minutes.
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36
(Alternatively, brown meringue with a blowtorch.)
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37
Serve immediately or refrigerate until ready to serve.
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38
They can be refrigerated for up to 2 days These also freeze wonderfully!
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39
They can be assembled and frozen up to 1 week in advance.
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40
Defrost for 20 minutes before broiling the tops and serving.
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41
- The crusts can be made, baked and frozen up to 2 weeks.
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42
- The curd can be made up to 3 days in advance and refrigerated.
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43
- The meringue can be made up to 1 day in advance and refrigerated.
