Preheat your oven to 350°F (175°C) and line a cupcake pan with paper liners.
Sift together cocoa powder, flour, baking powder, baking soda, and salt in a large mixing bowl until evenly combined and free of lumps.
In a separate bowl, whisk the eggs with vanilla extract until smooth and slightly frothy, then stir in the Greek yogurt and vegetable oil until the mixture is uniform and creamy.
Gradually add the wet ingredients to the dry ingredients, folding gently with a spatula until just combined. The batter should be glossy and thick but pourable.
Spoon the batter into the cupcake liners, filling each about two-thirds full to allow room for rising.
Bake in the preheated oven for 18–20 minutes, or until a toothpick inserted into the center comes out with moist crumbs and the tops have developed a crackly, matte finish.
Remove the cupcakes from the oven and let them cool in the pan for 5 minutes, then transfer to a wire rack to cool completely. The tops will crack beautifully as they cool.
Optionally, melt the dark chocolate and drizzle over the cooled cupcakes for an extra gooey chocolate surprise inside.
Once cooled, enjoy the tender, moist crumb with a crackly, chocolate-topped surface that reveals a gooey chocolate center when bitten.
