Preheat the oven to 180 C / Gas 4. Grease two sandwich tins.
Combine margarine and butter and beat well. Beat in the sugar and continue beating till light and creamy. Add the eggs, one at a time, stirring after each addition. Stir in the Nutella® and vanilla. Finally, stir in the flour. If the cake mixture is too thick, add a splash of milk. Divide the mixture between the two tins.
Bake the cakes till a skewer inserted in the centre comes out clean.
Put the cakes onto a the cooling rack, leave till cool. Ice if you wish.