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1
For the raspberry sauce, mix 1 cup of the raspberries, the preserves, water, and the sugar in a medium-size heavy saucepan (not uncoated aluminum.)
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2
Bring to a boil over moderately high heat, mashing the raspberries with a wooden spoon.
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3
Boil 1 minute.
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4
Remove from the heat.
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5
Strain the raspberry mixture through a fine strainer suspended over a bowl, pressing down on raspberries to release the juices.
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6
Discard the seeds.
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7
Stir the blueberries and the remaining 1 cup raspberries into the hot raspberry syrup.
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8
Cover and let stand until cool.
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9
Refrigerate until ready to use.
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10
For the cake, check that one rack is in the middle of the oven and heat the oven to 325 degrees.
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11
Pour the egg whites into the bowl in which you will be making the batter.
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12
If the pan has a removable bottom, do nothing to it.
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13
If it does not, lightly butter the bottom.
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14
Line the bottom with waxed paper or parchment paper cut to fit, and lightly butter the paper.
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15
Thoroughly mix the flour and 1/4 cup of the granulated sugar or 1/2 cup of the confectioners' sugar in a small bowl.
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16
Have all the ingredients and tools at hand.
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17
Beat the egg whites with an electric mixer on medium speed for about 2 minutes, until frothy and well broken up.
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18
Add the cream of tartar and increase the speed to medium-high.
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19
Beat until the whites lose their yellow cast, greatly increase in volume, and start to turn white.
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20
With the mixer running, slowly sprinkle the remaining 3/4 cup sugar over the whites.
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21
Beat until the whites become very thick, very glossy, and white, and the beaters leave a deep trail.
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22
Depending on the mixer, this need take only about 3 minutes total.
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23
Beat in the lemon juice and vanilla, just enough to mix.
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24
Reduce the speed to the lowest possible.
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25
Quickly sprinkle the flour sugar-mixture over the whites.
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26
As soon as it is all added, but not completely mixed in, stop the machine and remove the bowl.
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27
With a rubber spatula or a large metal spoon, complete mixing in the flour by folding or gently stirring.
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28
Stop just as soon as the flour seems blended in.
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29
With a rubber spatula, scrape the batter (9 cups) into the pan and spread evenly.
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30
Inscribe a circle deep in the batter to release any large air bubbles.
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31
Bake until no moist patches remain in the surface cracks, the cake springs back when touched, and a cake tester inserted in the center comes out clean, about 50 minutes for a 10 by 3-inch pan, 1 hour for a tube pan.
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32
Turn the pan upside down on a wire rack.
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33
Let cool completely.
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34
Loosen the edges (and tube) with a knife.
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35
Turn out the cake, loosen and remove the pan bottom, or peel off the paper.
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36
Store airtight 1 day at room temperature before serving or freezing.
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37
When serving, top cake with sauce and confectioners'sugar, if you wish.
