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1
Preheat oven to 250 F. and line a baking sheet with parchment paper.
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2
In a bowl with an electric mixer beat whites with salt until they hold soft peaks.
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3
Gradually beat in sugar and beat until meringue holds stiff, glossy peaks.
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4
Spread meringue 1/2 inch thick on parchment-lined baking sheet and bake in middle of oven 1 hour, or until firm to the touch.
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5
Turn off oven and let meringue stand 1 hour.
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6
Transfer meringue on parchment to a rack and cool.
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7
Peel off parchment and, working over a bowl, break meringue into 1/2- to 1-inch pieces.
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8
Meringue may be made 3 days ahead and kept in an airtight container in a cool, dry place.
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9
In a heavy saucepan bring cream, milk, sugar, zest, and salt just to a boil, stirring occasionally.
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10
In a bowl beat yolks until smooth.
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11
Add hot cream mixture to yolks in a slow stream, whisking, and pour into pan.
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12
Cook custard over moderately low heat, stirring constantly, until a thermometer registers 170 F. Pour custard through a sieve into a clean bowl and stir in lemon juice.
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13
Cool custard.
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14
Chill custard, its surface covered with plastic wrap, at least 3 hours, or until cold, and up to 1 day.
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15
Freeze custard in an ice-cream maker.
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16
Transfer ice cream to a bowl and fold in meringue.
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17
Transfer ice cream to an airtight container and put in freezer to harden.
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18
Ice cream may be made 1 week ahead.
