Preheat the oven to 200C/180C Fan/Gas 6. Line an 8" Square Pan.
Start by melting the dark chocolate: break up the dark chocolate and melt in the microwave in 20 second intervals, stirring in between to make sure it doesn’t burn. Set aside to cool whilst doing the rest:
Combine the melted butter, granulated sugar and light brown sugar in a large bowl/bowl of a stand mixer – on a medium speed for 3-5 minutes.
Add in the eggs and vanilla and mix again. Then, checking first that the chocolate isn't so hot as to cook the eggs, add it in and keep mixing.
Pour batter into the pan. Bake 30 minutes (should no longer be wobbly), then remove and let cool on a wire rack.
Make the frosting by combining all ingredients and a few drops pink food colour (if using) with an electric mixer on high speed. The result should be a thick pink buttercream - spreadable but only just! Add hot water, one teaspoon at a time to reach this consistency. (Adjust using more icing sugar or water as needed). Spread over the cool brownie layer.
Melt the chocolate for the topping together in a small bowl in the microwave, checking/stirring at 20 second intervals. Once fully melted, pour over the strawberry layer and spread evenly. Let set in the fridge for about an hour before slicing and serving!