Preheat oven to 350°F (180°C). Line a muffin pan with baking cups. Sift flour, baking powder and salt together into a bowl. Cream butter and sugar in a food processor until smooth.
Add an inch (2.5 cm) of water to a saucepan and bring to a simmer over medium heat. Place chocolate chips in a heatproof bowl and place over saucepan; heat while stirring until chocolate is melted.
Add melted chocolate to the butter and sugar mixture, and stir to combine. Add one egg at a time, beating well after each addition. Add one third of the flour and buttermilk, mix just until incorporated, and repeat with second and final portions.
Spoon cupcake mixture into baking cups until about 3/4 full. Bake in preheated oven for approx. 15 minutes or until an inserted toothpick comes out clean. Place cupcakes on wire rack and let cool completely.
To make frosting, cream butter with cream cheese, then add icing sugar, vanilla and milk, and beat to combine. Gently spread icing on cup cakes.
Place remaining chocolate chips in bowl and microwave on medium-high heat for approx. one minute or until melted. Spoon melted chocolate into pastry bag fitted with fine round tip.
Carefully pipe a pea-sized dot of chocolate in the center of the cupcake, then 2 rings around it. With a toothpick, drag the tip through the chocolate from the center dot to the edge. Repeat approx 8 times around the centre.