Heat whipping creamand 2 t. lemon rind in large saucepan over medium-low heat until hot. Add chocolate chips and cook 5 min or until melted, stirring constantly. Cool, cover and chill at least 5 hours.
Meanwhile, melt unsweetened chocolate and 1 T. lemon rind in small saucepan; let cool.
Stir together flour, baking powder, soda and salt. Set aside.
Beat butter until creamy; add sugar and beat until light and fluffy. Add eggs, 1 at a time, beating just until blended. Stir in vnilla. Add flour mixture alternately with yogurt, beginning and ending with dry things. Stir in melted unsweetened chocolate mixture just until blended. Divide batter among 3 lightly greased 9-inch round cakepans.
Bake at 350 for 25 min or till tests clean. Cool in pans on racks 10 minute Remove from pans and cool completely on racks.
Meanwhile, beat chilled whipping cream mixture at medium until soft peaks form. Be careful not to overbeat. Frost cake. Store in fridge.