Cake: Preheat oven to 350°F. Line bottom of 9-inch springform pan with parchment paper. Stir together ground almonds, baking powder and salt.
Using electric mixer, beat egg yolks with sugar for 2 to 3 minutes or until pale yellow; fold in butter and vanilla.
Using clean beaters, beat egg whites with cream of tartar until stiff peaks start to form. Fold almond mixture into egg yolk mixture, then fold in egg whites.
Scrape into prepared pan; smooth top. Bake for about 45 minutes or until cake tester inserted into center comes out clean. Let cool on rack for 15 minutes. Run knife around edge of pan; release cake from pan.
Assembly: Transfer cake to serving platter. In small saucepan, combine honey and cardamom over low heat; cook for about 5 minutes or until honey is thin, syrupy and fragrant. Using skewer, poke holes into top of cake. Pour honey over top; let stand for 10 minutes. Garnish with sliced almonds. Serve warm or let cool before serving.
To grind almonds, add to food processor; pulse until finely ground (be careful to avoid overprocessing, or you will make almond paste). Sift almonds to remove any bigger pieces.
Serve cake with dollop of Greek yogurt if desired.