Brownie-Bottom Lemon Cheesecake

PreparationFor crust: Preheat oven to 350°F. Spray inside of 9-inch-diameter springform pan with 2 3/4-inch-to 3-inch-high sides with nonstick spray. Whisk flour, cocoa, and salt in small bowl; set aside. Combine chocolate and butter in medium metal bowl; place bowl over saucepan of simmering water and stir until melted and smooth. Remove bowl from over water. Add both sugars to chocolate mixture and whisk until blended. Let cool until mixture is barely lukewarm, about 10 minutes. Whisk egg and vanilla into chocolate mixture. Fold flour mixture into chocolate mixture. Spread brownie batter evenly over bottom of prepared pan. Bake brownie crust until top looks slightly cracked and tester inserted into center comes out with some moist crumbs attached, about 20 minutes. Transfer pan to rack; cool crust to room temperature, about 30 minutes. Maintain oven temperature. For filling: Place pan with cooled crust on rimmed baking sheet. Using electric mixer, beat cream cheese in large bowl until smooth. Add sugar, flour, lemon peel, and lemon juice; beat until smooth. Add eggs and yolks, 1 at a time, beating just until incorporated after each addition. Beat in 1/2 cup sour cream and whipping cream. Pour filling over brownie crust in pan; smooth top. Bake cake until puffed, light golden, and set around edges (center will still move slightly when pan is gently shaken), about 1 hour 20 minutes. Remove cake from oven. Maintain oven temperature. For topping: Spoon 1 cup sour cream in dollops over top of cake, then spread evenly over top with offset spatula. Return cake to oven and bake 5 minutes. Run small sharp knife around sides of cake to loosen. Place pan with cake directly in refrigerator and chill uncovered overnight (cake may sink in center). DO AHEAD: Can be made 2 days ahead. Keep chilled. Remove pan sides from cake. Run thin sharp knife between pan bottom and crust to loosen. Using 2 metal spatulas as aid, transfer cake to platter. Garnish top edge of cake with chocolate curls and lemon slices.

PreparationFor crust: Preheat oven to 350°F. Spray inside of 9-inch-diameter springform pan with 2 3/4-inch-to 3-inch-high sides with nonstick spray. Whisk flour, cocoa, and salt in small bowl; set aside. Combine chocolate and butter in medium metal bowl; place bowl over saucepan of simmering water and stir until melted and smooth. Remove bowl from over water. Add both sugars to chocolate mixture and whisk until blended. Let cool until mixture is barely lukewarm, about 10 minutes. Whisk egg and vanilla into chocolate mixture. Fold flour mixture into chocolate mixture. Spread brownie batter evenly over bottom of prepared pan. Bake brownie crust until top looks slightly cracked and tester inserted into center comes out with some moist crumbs attached, about 20 minutes. Transfer pan to rack; cool crust to room temperature, about 30 minutes. Maintain oven temperature. For filling: Place pan with cooled crust on rimmed baking sheet. Using electric mixer, beat cream cheese in large bowl until smooth. Add sugar, flour, lemon peel, and lemon juice; beat until smooth. Add eggs and yolks, 1 at a time, beating just until incorporated after each addition. Beat in 1/2 cup sour cream and whipping cream. Pour filling over brownie crust in pan; smooth top. Bake cake until puffed, light golden, and set around edges (center will still move slightly when pan is gently shaken), about 1 hour 20 minutes. Remove cake from oven. Maintain oven temperature. For topping: Spoon 1 cup sour cream in dollops over top of cake, then spread evenly over top with offset spatula. Return cake to oven and bake 5 minutes. Run small sharp knife around sides of cake to loosen. Place pan with cake directly in refrigerator and chill uncovered overnight (cake may sink in center). DO AHEAD: Can be made 2 days ahead. Keep chilled. Remove pan sides from cake. Run thin sharp knife between pan bottom and crust to loosen. Using 2 metal spatulas as aid, transfer cake to platter. Garnish top edge of cake with chocolate curls and lemon slices.