Pre-heat the oven to 180 C / Gas 4. Grease a muffin tin, or line with paper cases.
Melt the butter and chocolate together on the hob. Once its melted, take off the heat and add the sugar. Transfer to a large mixing bowl and beat in the eggs and vanilla.
Mix together the flour, bicarb, cocoa and salt. Sift into the chocolate mixture and mix well. Gradually add the milk and stir till well combined, then fold in the chocolate chips. Spoon into a prepared cases.
Bake for 20 to 25 minutes, or until the tops spring back when touched. Cool on a wire rack.
Microwave white chocolate and double cream on full power in 30 second intervals till white chocolate is melted.
Cream the softened butter with the icing sugar. Add in the white chocolate mixture and beat well. If needed, add more icing sugar till the icing reaches your desired consistency. Let the icing set in the fridge for 1 hour.
When cakes are cool and icing is set, pipe the icing onto the cupcakes. Enjoy!