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1
For the cake, adjust oven rack to middle position and preheat oven to 350u00b0F.
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2
Sift together sifted flour and 3/4 cup sugar into large bowl. Make well in center and add egg yolks, water, lemon juice, and vanilla extract. Whisk together until combined.
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3
In separate clean and dry bowl, whip egg whites, cream of tartar, and salt with whisk attachment on medium speed until soft peaks form, about 2 minutes. Gradually add remaining 3/4 cup sugar and continue whipping until stiff peaks form, 2 to 3 minutes longer. Stir 1/3 of egg whites into batter with rubber spatula until fully incorporated. Gently fold in remaining egg whites.
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4
Pour patter into ungreased tube pan. Cut through batter with a knife, swirling it gently back and forth to break up large air bubbles. Bake until top springs back when you press down on it, 50 to 55 minutes. Invert pan onto cooling rack and cool completely, 2 to 2 1/2 hours. Prepare the brittle topping while the cake cools.
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5
Line large baking sheet with parchment paper. Grease parchment with butter.
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6
In medium heavy-bottomed saucepan, combine almonds, sugar, corn syrup, water, and espresso powder. Cook over medium heat, stirring, until sugar dissolves, 2 to 3 minutes. Increase heat to medium-high and boil, stirring frequently, until mixture is thick and deep amber and temperature reads 295u00b0F on candy thermometer, 8 to 12 minutes.
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7
Remove from heat and immediately stir in baking soda and salt. Pour mixture onto prepared baking sheet and spread into even layer (roughly, an 8- by 8-inch square) with wooden spoon.
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8
Let brittle cool and harden on sheet, 30 to 45 minutes. When cool, using a meat mallet or wooden spoon, break brittle into coarse pieces and reserve.
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9
Once cake is cool, invert the pan. Run a long, flexible knife along the edge of the cake and along the tube. Turn the cake over; it should fall right out.
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10
For the filling and assembly: Whip cream, confectioners' sugar, and vanilla in a chilled bowl until soft peaks form, 2 to 3 minutes.
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11
Slice cake crosswise with a serrated knife into four layers. Spread half of whipped cream evenly among layers and use the remainder to coat the top and outside of the cake. Press brittle onto cake and serve.
