Batter 2 9-inch round cake pans,lined with parchment or wax paper,& butter & flour the paper, shaking off excess
In a bowl, sift the flour, baking soda and salt
In another bowl, beat butter with an electric mixer until smooth
Add the sugar a little at a time & beat mixture until light & fluffy
Beat in eggs, orange zest & vanilla
Beat in 1/3 of the dry ingredients alternately with 1/2 of the buttermilk until combined well.Add half the remaining dry ingredients & the remaining buttermilk & beat until combined well
Finally, beat in the remaining dry ingredents until mixture is smooth
Evenly divide the batter between the pans
Smooth the surface, rap each pan on the counter to expel any air pockets or bubbles
Bake for 45 minutes, or until a cake tester inserted into the center comes out clean
In a bowl, stir together the orange juice & sugar until sugar is dissolved.
Poke holes in cake with toothpick, spoon the syrup over each layer, let layers cool completely
In a small saucepan, on med heat,heat marmalade until melted.Let cool 5 minutes
Wisk heavy cream with the sugar, until forms firm peaks. Add sour cream, a little at a time, whisk until mixture is spreading consistency
Arrange one of the layers on a cake plate and carefully peel off the wax paper spread 2/3 of the marmalade over the top, smoothing it into an even layer. Invert the remaining layer onto the top of the first layer, peel off wax paper, spoon the remaining marmalade on the center of it, leaving a 1 1/4 inch border around the edge Frost the sides & the top boarder with the frosting, leaving the marmalade on top of the cake exposed. Or,if you prefer, frost entire cake, adding marmalade as a garnish on top. Chill 2 hrs before serving.