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1
Preheat the oven to 400F (200C).
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2
Fit the pastry into a 9 inch (23cm) tart pan with a removable bottom, fitting it tightly into the corners, and trim the excess dough.
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3
Prick the dough with a fork.
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4
Line with wax paper and fill with baking beans.
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5
Chill for 30 minutes.
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6
Place on a baking sheet and bake for 10 minutes, until the dough looks set.
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7
Remove the paper and the beans and bake until the dough is crisp and golden brown, about 10 minutes more.
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8
Transfer to a wire rack.
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9
Reduce the oven temperature to 350F (180C).
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10
Meanwhile, to make the filling, grate the zest from 2 of the lemons.
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11
Juice the lemons: you should have 3/4 cup of juice.
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12
Whisk 3/4 cup of the sugar, the egg yolks, and cornstarch together in a bowl until the mixture is pale yellow.
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13
Gradually whisk in 1 cup water and the lemon juice.
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14
Add the butter.
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15
Pour into a saucepan.
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16
Bring to a simmer over medium heat, stirring constantly, until simmering and thickened.
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17
Reduce the heat to low and let bubble for 30 seconds.
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18
Strain through a wire sieve.
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19
Stir in the zest.
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20
Spread evenly in the tart shell.
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21
Beat the egg whites in a large bowl with an electric mixer until foamy.
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22
Add the cream of tartar and beat until soft peaks form.
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23
Beat in the remaining 1/2 cup sugar, a tablespoon at a time, until the meringue is thick and glossy.
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24
Spread the meringue over the hot filling, being sure that it touches the pie crust on all sides.
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25
Place the tart on a baking sheet.
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26
Bake for 1215 minutes until the meringue is tinged light brown.
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27
Transfer to a wire rack and let cool completely.
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28
To slice, dip a thin, sharp knife into a tall glass of hot water before each slice.
