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1
Position a rack in the middle of the oven and heat the oven to 275 degrees F. Lightly coat a 9-inch springform pan with cooking spray. Spread nutes on a baking sheet and toast until lightly golden, about 10 minutes. Transfer nuts to a plate to cool. Increase the oven to 325 degrees F.
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2
In a large metal bowl, with an electric mixer at high speed, beat egg whites until frothy, about 1 minute. Add cream of tartar and continue to beat until stiff peaks form, about 3 minutes longer. Set aside.
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3
In a separate bowl large bowl, with an electric mixer and medium speed, beat egg yolks, 1/3 cup of the sugar substitute, and vanilla for 1 minute. Add ricotta and zest, and beat until smooth.
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4
Gently fold one-third of the whites into the yolk mixture, then add the rest of the whites and gently fold in until well combined. Pour batter into the prepared pan, place the pan on a baking sheet, and bake until cake is golden and mostly set, about 1 hour 10 minutes. Remove cake from oven and cool on a rack for 20 minutes.
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5
In a small saucepan, combine lemon juice and remaining 1 tsp. sugar substitute; bring to a simmer over low heat. remove from the heat and gently brush the surface of the cooled cake with two-thirds of the warm lemon mixture; drizzle remaining mixture into the cracks. Sprinkle the top with pine nuts.
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6
Cook cake completely, then run a knife around the edge before releasing from pan. Chill, loosely covered, for 4 hours or overnight. Serve chilled.
