Preheat oven to 350°. Line bottoms of 2 greased 9-in. round baking pans with parchment; grease parchment., Cream butter and sugar until light and fluffy, 5-7 minutes. Add eggs and egg yolks, 1 at a time, beating well after each addition. Beat in lemon zest and juice. In a small bowl, mix sour cream and milk. In another bowl, whisk together flour, salt, baking powder and baking soda; add to creamed mixture alternately with sour cream mixture., Transfer to prepared pans. Bake until a toothpick inserted in center comes out clean, 24-28 minutes. Cool in pans 10 minutes before removing to wire racks; remove parchment. Cool slightly., For syrup, in a small saucepan, combine sugar and lemon juice. Bring to a boil; cook until liquid is reduced by half. Cool completely., For frosting, beat cream cheese and butter until smooth; beat in confectioners’ sugar, lemon juice and salt until blended., Using a long serrated knife, cut each cake horizontally in half. Brush layers with warm syrup; cool completely., Place 1 cake layer on a serving plate; spread with 1 cup frosting. Repeat layers twice. Top with remaining cake layer. Frost top and sides with remaining frosting. If desired, top with lemon slices or edible flowers. Refrigerate leftovers.