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1
Let egg whites stand at room temperature 1 hour.
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2
Preheat oven to 250 F. Line 2 baking sheets with parchment paper and draw three 10- by 4 1/2-inch rectangles on parchment (2 on one sheet and 1 on other).
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3
Turn parchment over.
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4
In a large bowl with an electric mixer beat whites with cream of tartar and a pinch salt until they hold soft peaks.
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5
Gradually add sugar, beating, and beat until meringue holds stiff, glossy peaks.
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6
Transfer meringue to a pastry bag fitted with a 1/2-inch fluted tip and pipe evenly onto parchment rectangles, filling them in.
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7
(Alternatively, divide meringue among parchment rectangles, spreading with a spatula to fill them in.)
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8
Bake meringue layers in upper and lower thirds of oven, switching positions halfway through baking, 1 hour, or until crisp and firm.
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9
(If weather is humid, cooking time may be longer.)
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10
Cool meringue layers completely on baking sheet in turned-off oven or on a rack and carefully peel off parchment.
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11
Meringue layers may be made 1 day ahead, wrapped well in plastic wrap or sealed in an airtight container, and stored in a cool, dry place.
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12
In a heavy saucepan stir together puree ingredients and simmer, stirring occasionally, until rhubarb is softened, about 12 minutes.
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13
Cool mixture slightly and in a blender or food processor puree until smooth (use caution when blending hot mixtures).
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14
Transfer puree to a bowl and cool.
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15
Puree may be made 2 days ahead and chilled, covered.
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16
Bring puree to room temperature before proceeding.
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17
Lightly whip heavy cream.
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18
On a large platter arrange 1 meringue layer and spread evenly with 1/2 cup rhubarb puree.
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19
Spread half of whipped cream evenly over puree and top with 3/4 cup raspberries.
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20
Repeat procedure with another meringue layer, 1/2 cup puree, remaining whipped cream, and 3/4 cup raspberries.
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21
Top with remaining meringue layer.
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22
Garnish cake with remaining cup raspberries and serve with rhubarb raspberry sauce.
