3tablespoon45ml full fat sour cream or plain yogurt(or replace the combined sour cream and milk with ½ cup total of buttermilk - see FAQ above in the article)
Sift flour, cocoa powder, baking powder and baking soda into a large bowl. Add both sugars and salt and whisk until thoroughly combined and there are no lumps of brown sugar remaining.
Add oil, melted butter, eggs, sour cream and vanilla and begin whisking gently until just combined. Start by poking the eggs to break up the yolks so they blend easier. The mixture will still look dry and thick at this stage.
Warm the milk gently in the microwave until just lukewarm and add it to the bowl. Continue to whisk until the batter is completely smooth. Fold in chocolate chips if desired.
Pour or spoon the batter into the liners filling them no more than two-thirds full (this is important to avoid spilling over the sides or sinking). Bake for 17-20 minutes until a toothpick inserted in the center comes out clean. Transfer cupcakes to a wire rack to cool completely.
Make the glaze. Combine chopped semisweet chocolate and cream in a medium bowl and place in the microwave for 1 ½ minutes at 50% power. Once you see the cream start to bubble, it's ready. Stir gently until smooth and glossy, then let cool until thick but still glossy and not totally set. Dip the tops of cooled cupcakes into the glaze and then place on a tray. Place the tray in the fridge to set the glaze before piping on the frosting.
Make the frosting. Prepare the frosting as per the instructions here.
Pipe the chilled cupcakes with the frosting and then decorate with chocolate sprinkles.