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1
Bring about 2-inches of water to a simmer in a large saucepan.
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2
In the bowl of a mixer, fitted with a whisk attachment (or using a hand mixer), whip the eggs and sugar together until very light yellow and fluffy.
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3
Mix in the lemon juice and lemon zest.
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4
Rest the mixing bowl in the saucepan, with the bowl's base resting above, not in, the simmering water (pour out some water if necessary).
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5
Cook, whisking occasionally, until the mixture is thickened and custard-like, about 10 minutes.
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6
Meanwhile, half-fill a large bowl with ice and cover with cold water.
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7
Remove the bowl with the custard in it from the hot water and whisk in the butter until melted.
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8
Rest the bottom of the bowl in the ice bath and let cool, folding the mixture occasionally to cool and thicken it.
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9
In a mixer, fitted with a whisk attachment (or using a hand mixer), whip the cream until stiff.
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10
Fold into the cooled lemon custard.
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11
Cover and refrigerate until ready to serve.
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12
(The recipe can be made up to this point and kept refrigerated up to 3 days in advance.)
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13
Heat the oven to 350 degrees F.
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14
Flour a work surface and lay out the puff pastry.
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15
Roll the sheets lightly with a rolling pin until smooth and flattened.
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16
Use your large cookie cutter to cut out rounds from the puff pastry.
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17
Hollow out the centers by pushing halfway down with your small cookie cutter.
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18
Do not pull out the centers yet; you'll do that after they are baked.
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19
Arrange on an un-greased cookie sheet and bake until golden brown, 15 to 20 minutes.
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20
After 10 minutes, rotate the pan to ensure even cooking.
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21
When baked, immediately remove to a wire rack and let cool to room temperature.
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22
Cut around the centers with a paring knife to loosen, but don't cut all the way through to the bottom.
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23
You want to leave a thin layer of pastry to hold the filling.
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24
Pull out the centers to make a hollow in the center of each pastry round.
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25
Not more than 4 hours before serving, spoon or pipe a generous dollop of custard into each pastry round.
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26
Sprinkle the custard with chopped pistachios.
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27
Serve within 4 hours.
