Position a rack in the middle of the ovem and heat to 275. Lightly coat a 9-inch springform pan with cooking spray.
Spread nuts on a baking sheet and toast until lightyl golden, abotu 10 minutes. Transfer nuts to a plate and cool. Increase oven to 325.
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 more. Set aside.
In a separate large bowl, with an electric mixer at medium speed, beat egg yolks, 1/3 cup sugar sustitute and vanilla for 1 minute. Add ricotta and zest and beat until smooth.
Gently fold about 1/3 of the egg whites into the egg yolks 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 hr and 10 minutes. Remove cake from oven and cool on rack for 20 minutes.
In a small saucepan, combine lemon juice and remaining 1 t of the sugar substitute; bring to a simmer over low heat. Remove from the heat and gently brush the surface of the cake with two-thirds of the warm lemon mixture; drizzle remaining mixture into the cracks. Sprinkle the top with pine nus.
Cool cake completely, then run a knife around edge before releasing from the pan. Chill covered for 4 hours or overnight. Serve chilled.