Preheat the oven to 180 C / Gas 4. Grease 2 loaf tins; line tins with baking parchment.
Combine the baking powder and soured cream in a small bowl and set aside.
In a mixing bowl, combine the flour and salt and mix well.
In a separate bowl, beat together the butter and sugar until fluffy. Add eggs, one at a time; beat until pale and creamy. Add the lime juice, zest, soured cream and flour; mix until well incorporated. Spoon the mixture into the prepared loaf tins.
Bake the cake for 45-50 minutes or until a skewer inserted into the middle of the loaf cakes comes out clean. Set the cakes aside to cool in the tin for 5 minutes; remove cakes from the tin and cover with a clean tea towel while you make the icing.
Lime drizzle icing:
Mix 2 tablespoons of lime juice with 2 tablespoons of the icing sugar; continue to add icing sugar in batches until the icing is smooth and glossy.