Preheat oven to 350°F.
Line an 8x8 square baking pan with greased wax paper, leaving a 2-inch overhang on each side.
Add 4 ounces of chopped chocolate and butter to a medium bowl and microwave in 30-second increments until melted.
Whisk in the sugars and mix well.
Add the eggs and vanilla and stir until blended.
Stir in the flour, salt and baking powder until combined.
Pour a very thin layer of batter into prepared baking pan and then dot with 16 Ferrero Rocher candies, spacing evenly.
Bake for 20-22 minutes.
Cool completely on a wire rack.
Add remaining chopped chocolate to a heat-proof bowl.
Add heavy cream to a glass measuring cup and microwave for 1 minute until steaming.
Pour cream over the chocolate and let sit for 1 minute.
Whisk together until chocolate is blended and melted.
Pour chocolate over the top of the brownies.
Garnish with chopped candies.
Let set before slicing into squares.