In a bowl, mix together the curd and baking soda. Set it aside.
In another bowl, mix together the melted butter and warm milk. Mix well. Then add the caster sugar and the Buttercream flavour. Mix mix mix. Now add the curd mixture and mix some more.
Sift in the flour and baking powder. Using a spatula, fold gently.
In a baking tin lined with parchment paper, bake at 180C for about 40-42 minutes.
