Set up TWO double boilers on the stove—to achieve the swirl you need to work simultaneously. (My mom gave me a real double boiler for Christmas after seeing my rigged up version in my Christmas Bark post, but you can just make your own if you don't have one.) I place a small sauce pan on the stove and fill it with a few inches of water. Then I place a glass heat safe bowl on top (make sure the water isn’t touching the bowl). Then I heat it on medium low heat—do not let the water boil.
Line a large jelly roll pan with parchment paper and set aside. Crush the raspberry pieces (I just squeezed them from the outside of the bag) and set aside.
Place your dark chocolate in the bowl of one double boiler and stir occasionally until melted. Place your white chocolate in the other and stir until completely melted. Add 1 t of coconut oil (if using) into each bowl and stir it in completely. Add the espresso powder into the dark chocolate and mix again until dissolved and well incorporated. Add the vanilla extract into the white chocolate and mix until well incorporated. Remove from heat.
Carefully pick up the dark chocolate bowl using an oven mitt. With your other hand, use a towel to wipe the bottom of the bowl so that the condensation doesn’t drip out onto the prepared tray. Pour the dark chocolate onto the prepared tray and use a spatula to spread the chocolate around. Now pick up the white chocolate bowl and wipe the same way. Spoon the white chocolate around the dark chocolate. Then using the tip of a pointed knife, or a skewer, swirl the white chocolate through the dark chocolate until you like the design. Resist the urge to over swirl—you don't want milk chocolate!
Sprinkle with raspberry pieces and set it into the freezer for at least 10 minutes to firm up completely.
Once completely solid, use a sharp knife to break up the chocolate into chunks. I continue to store my chocolate in the freezer until ready to eat. It comes up to room temperature very quickly! Enjoy!