Preheat the oven to 350 F (180 C) and line a muffin tin with cupcake liners.
Sift the flour, granulated sugar, cocoa powder, baking powder, baking soda and salt into a large mixing bowl. In a separate bowl or large liquid measuring cup, whisk together the sour cream, milk, brown sugar, oil, egg, and extracts. Add this all at once to the dry mixture and then whisk by hand until the batter is smooth, about 2 minutes. Stir in the chocolate chips.
Use an ice cream scoop to portion the batter into the prepared tin evenly and bake for about 25 minutes, until a tester inserted in the centre of a cupcake comes out clean. Allow the cupcakes to cool on a rack, in the tin completely before frosting.
For the frosting, beat the butter until fluffy using electric beaters.
Add 1 cup (130 g) of the icing sugar and beat until smooth (start on low speed and then increase to medium high to avoid an icing sugar dust storm!) Add the cocoa powder, beat in on low speed and then add the melted chocolate, cream and extracts and beat on low speed then increasing to medium high, until light and fluffy, adding the remaining Â˝ cup (65 g) of icing sugar if needed. Use the frosting while at room temperature.