- With the rack in the middle position, preheat the oven to 180 °C (350 °F). Line 16 muffin cups with paper or silicone liners. Set aside.
- In a bowl, combine flour, cocoa powder, baking powder and salt. Set aside.
- In another bowl over a double boiler or in the microwave oven, melt chocolate and butter. Remove bowl from the double boiler. Let cool.
- In a measuring cup, combine milk and vinegar. Set aside.
- In a bowl, beat egg and sugar until the mixture lightens. Add cooled chocolate mixture and combine well. Add dry ingredients alternately with the milk mixture until smooth.
- With a 60 ml (¼ cup) ice cream scoop, spoon batter into cups. Bake for about 22 minutes or until a toothpick inserted in the centre of a cupcake comes out clean. Cool on a wire rack.
- Place chocolate in a bowl. Set aside.
- In a small saucepan or in the microwave oven, bring cream and corn syrup to a boil. Pour over chocolate. Let melt for 1 minute without stirring.
- With a whisk or spatula, combine until smooth. Refrigerate for 45 minutes, stirring regularly, or until spreadable. Warm for a few seconds in the microwave oven, if necessary.
- With an offset spatula or pastry bag fitted with a plain or fluted tip, frost cooled cupcakes.