Preheat the oven to 325°F.
Sift the flour, cocoa powder, baking powder and salt into a large mixing bowl. Set aside.
Place the butter and sugar in a large stand mixer fitted with a paddle attachment. Cream the butter and sugar together until light and fluffy.
Add the eggs one at a time to the butter/sugar mixture, waiting for each egg to be fully integrated before adding the next one. Once all the eggs are integrated, add the vanilla extract.
Add half of the flour mixture to the butter/egg mixture. Wait until the batter is uniform, then add half of the yogurt. Add the remaining half of the flour mixture, followed by the last of the yogurt.
Turn off the mixer and remove the mixing bowl. Using a rubber spatula, fold the melted chocolate into the batter. Add the peppermint patty pieces and stir until even dispersed.
Pour the batter into an 8x8 inch greased baking pan lined with parchment paper. Transfer the brownies to the oven and bake for 30 minutes.
Let the brownies sit in the pan for 10 minutes before attempting to remove them.
Using the edges of the parchment sling, transfer the brownies to a cooling wrack and let cool for 10 minutes more.
Cut the brownies into 9 pieces while still warm.