For the chocolate coating: Heat the dark chocolate and butter in a double boiler until completely melted and smooth. Pour into a small ramekin.
Press a skewer or toothpick into the top end of each strawberry. Dip one strawberry into the chocolate, swirling it around until coated. Gently shake off the excess. Place the skewer on the edge of a table and weigh down the end of the skewer with a heavy object. Allow the excess chocolate to drip off onto the floor (place some parchment paper on the floor to catch the drips!). Repeat with the remaining strawberries. They should take about 15 minutes to set at room temperature. If it is a hot day, set up a little drip station in the fridge and allow them to cool in there!
For the decorations: Once the chocolate has set, put the strawberries on a wire cooling rack. Melt the milk chocolate and white chocolate in separate bowls in the microwave until smooth. Transfer the melted chocolate to 2 separate piping bags and allow it to cool for 5 minutes.
Drizzle the melted chocolate over the strawberries to decorate. Spray a few with the gold luster dust spray to coat, if using. Place the strawberries in the fridge until the coating has set (about 5 minutes), then serve.