First make the brownies: Preheat the oven to 180 degrees C and grease and line a 9x9 in baking tin.
Place ¾ of the cooked sweet potatoes into a blender or food processor and blend until smooth. Add in the other brownie ingredients and blend again to form a smooth, quite thick batter.
Scrape out the mixture and spread out evenly. Bake for 25 minutes until firm. Leave to cool in the tin.
Meanwhile make the frosting: Place the remaining cooked sweet potatoes into a blender or food processor and blend with the other ingredients until thick and smooth. Place into a bowl or container and keep in the fridge until needed.
Finally make the chocolate hearts: Gently melt the coconut oil and almond butter then whisk in the Natvia and cacao or cocoa powder. Sprinkle some freeze-dried raspberries into the bottom of a mini heart-shaped tin (it should make around 20 small hearts) then pour the chocolate mixture into each to reach the top. Chill for at least 2 hours to set.
Once the brownies have cooled, remove the whole thing from the tin and place on a chopping board. Spread the frosting over the top evenly in a generous layer. Cut into 9-12 pieces. Pop out some chocolate hearts and place one on top of each piece. Enjoy!