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1
Preheat oven to 275F.
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2
Draw 3 (14- by 3-inch) rectangles, about 3/4 inch apart, on parchment.
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3
Turn paper over (rectangles will be visible) and put it on a lightly buttered large baking sheet.
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4
Beat whites with a pinch of salt in a large bowl with an electric mixer at medium speed until they hold soft peaks.
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5
Beat in sugar, 1 tablespoon at a time, then increase speed to high and continue beating until whites hold stiff glossy peaks, about 4 minutes with a standing mixer or 8 to 10 minutes with a handheld.
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6
Transfer meringue to pastry bag fitted with 1/3-inch tip and fill in rectangles completely.
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7
Gently smooth tops, then bake in middle of oven until firm and very pale golden, 45 to 60 minutes.
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8
Slide meringue layers (on parchment) onto a large rack.
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9
Cool completely, then carefully peel off parchment.
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10
Melt butter with cornstarch, passion-fruit pulp, and 3/4 cup sugar in a 2-quart heavy saucepan over moderately low heat, stirring until sugar is dissolved.
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11
Whisk together whole egg and yolks in a large bowl until combined, then add butter mixture in a stream, whisking.
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12
Transfer mixture to saucepan and cook over moderately low heat, whisking constantly, until thick enough to hold mark of whisk and first bubble appears on surface, 3 to 5 minutes.
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13
Transfer curd immediately to a metal bowl set in a larger bowl of ice and cold water and cool, stirring occasionally, until cold.
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14
Beat cream with remaining 2 tablespoons sugar with electric mixer until it just holds stiff peaks.
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15
Fold 2 cups whipped cream into curd gently but thoroughly to form a mousse (for filling and icing).
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16
Transfer 3/4 cup whipped cream to a small bowl and reserve, chilled, for cream layer.
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17
Fold 1/2 cup mousse into remaining whipped cream, then transfer to cleaned pastry bag fitted with 1/8-inch tip and reserve, chilled, for decorative icing.
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18
Arrange 1 meringue layer, flat side down, on platter and spread evenly with 3/4 cup mousse.
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19
Cover with another meringue layer and spread evenly with reserved whipped cream.
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20
Cover with remaining meringue layer, flat side up, and spread remaining mousse evenly over top and sides of cake, smoothing with a cake spatula.
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21
Pipe icing decoratively on top of cake, then freeze, uncovered, until firm, at least 3 hours.
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22
About 1 hour before serving, put cake in refrigerator to soften slightly.
