Preheat your oven to 350°F (180°C).
Line and lightly grease a 6-inch square baking pan with parchment paper.
In another saucepan, melt the butter and sugars over low heat. Add the milk and turn off the heat.
Add the chocolate and stir until melted and smooth. Mix in the yogurt.
In a large bowl, sift together the flour and cocoa powder.
Pour the wet ingredients into the dry ingredients and mix until combined.
Fold in the raspberries.