In a mixing bowl whisk together the greek yogurt and powdered sugar until the sugar is dissolved. Check by rubbing the mixture in between your fingers.
Melt the chocolate using the double boiler method. Add in the bowl the chopped chocolate and butter. Stir until the chocolate is fully melted and combined.
Take the bowl of the melted chocolate and add this mixture to the yogurt-sugar mixture. Mix well.
Take flour, baking soda, and salt and sieve everything directly on top of your wet ingredients. Fold the batter to form a thick brownie batter.