For the brownies: Preheat the oven to 350 degrees F. Position a rack in the lower third of the oven.
Melt the chocolate and then pour it in a large bowl. Stir in the butter and the superfine and Demerara sugars, adding them in stages and beating each time with a wooden spoon until well mixed. Add the eggs, one at a time, again beating the mixture after each addition. Stir in the vanilla. Gently fold the flour into the chocolate mixture, and then fold in a pinch of salt.
Scrape the batter into heart-shaped silicone molds (see Cook's Note) sprayed with nonstick spray. Bake until the brownies have a nice, shiny top, and a cocktail stick inserted into the center comes out with a few crumbs, 20 to 25 minutes.
Place on a cooling rack, and let cool completely before removing the brownies from the molds.
For the peanut butter topping: Mix together the peanut butter, milk and grated white chocolate; top the brownies with spoonfuls of the mixture and garnish with shaved white chocolate. Leave out at room temperature.
You can make these brownies in one big tray (so, not in molds). If so, increase the cook time by about 10 minutes; you'll know it's done when the brownie starts moving away from the pan easily.