Place 12 large muffin cases in a cupcake tray.
In a large bowl, combine the plain flour, cocoa, baking powder, soft brown sugar, and a pinch of salt. Use a whisk to break up any lumps of sugar.
In a separate bowl, mix together the eggs, melted salted butter, sunflower oil, yogurt, and vanilla extract.
Pour the wet ingredients into the bowl of dry ingredients. Whisk until the batter is smooth and well combined.
Divide the batter evenly between the 12 muffin cases.
Place the cupcake tray on the middle shelf of the preheated oven. Bake for 17 to 18 minutes, or until a skewer or cocktail stick inserted into the center of a cupcake comes out with a few cake crumbs stuck on it, indicating they are done.
Allow the cupcakes to cool in the tray for a few minutes, then transfer them to a wire rack to cool completely. Once cooled, enjoy them as they are or with your favorite toppings or frostings.