Sieve all-purpose flour, cocoa powder and baking powder a couple of times until combined well.
In a microwave safe bowl, add dark chocolate and butter. Microwave for a minute or so until the butter and chocolate melts. Mix them well until smooth. Alternatively, melt chocolate along with butter in a double boiler (place the bowl with chocolate and butter over hot boiling water)
In another bowl, cream curd/yogurt along with sugar until it is smooth. Add baking soda and vanilla essence, mix well. Let this stay for a couple of minutes until the mixture becomes frothy.
To this curd mixture, add melted chocolate mixture and mix until smooth.
Now combine the wet and dry ingredients. Fold them gently until combined properly.
Scoop out the mixture and fill the silicon cupcake moulds until 3/4th, leveling them as you go.
In a preheated oven, bake them at 180°C for 6-8 minutes only. The edges and top should look baked.
Once removed from oven, wait for 3-4 mins and gently flip them down. Carefully peel off the silicon mould. When the cake is cut, center should gooey and chocolatey.