Make the brownies:

1. Preheat your oven to 350°F (180°C). Line an 8-inch square baking pan with parchment paper.
2. Melt the butter and chopped chocolate together in the microwave or over a double boiler until smooth and fully melted.
3. In a large bowl, whisk together the powdered sugar, brown sugar, eggs, and vanilla using a hand mixer for 1–2 minutes until the mixture looks smooth and slightly fluffy.
4. Pour in the melted chocolate and butter, and mix again for about 1 minute until fully combined.
5. Add the flour, cocoa powder, and salt. Use a spatula or wooden spoon to gently mix until smooth and well blended.
6. Pour the batter into the prepared pan and smooth the top.
7. Bake for 15–20 minutes. Check doneness by inserting a toothpick or knife in the center—it should come out with a few moist crumbs, not dry. The center should still feel soft.
8. Let the brownies cool completely in the pan.

Make the chocolate ganache:

1. Place the chopped chocolate in a medium bowl.
2. Heat the heavy cream in a small saucepan until it just starts to simmer.
3. Pour the hot cream over the chocolate and let it sit for a minute, then stir with a spatula until smooth. If needed, microwave it for a few seconds to fully melt.
4. Pour the ganache over the cooled brownies and spread into an even layer.
5. Top with Smarties or candy-coated chocolates.
6. Chill in the fridge for at least 1 hour before slicing into 16 squares with a sharp knife.