Cake: Preheat the oven to 180 degrees C. Butter and flour two 20cm round cake tins.
Sift together flour, baking powder and bicarb into a large bowl.
In a food processor, process sugar with the butter then add three eggs; continue processing until fluffy. Stir into flour in three parts, alternating with buttermilk. Stir in the lemon juice and zest. Pour cake mixture into prepared cake tins.
Bake for 30 to 40 minutes, or until a skewer inserted into the centre comes out clean. Remove from tin, and set aside to cool.
Filling: Starting with a clean and cold metallic or glass bowl, beat the cream until stiff peaks form. Fold in 2 tablespoons lemon juice and 1 tablespoon lemon zest.
Spread lemon curd on top of one cake layer. Place second cake layer upside-down on top of lemon curd. Top cake with whipped cream.