Either line a baking sheet/tray with a silicone mat or you can also use a plate that works to go in the freezer.
Using a small cookie scoop, if possible, or a tablespoon measure, take balls of the chilled filling, around 1 tablespoon each, and use your hands to form in to balls. Place them on the silicone mat/plate then repeat until you have used all of the mixture. Put in the freezer to firm up for around 15 minutes.
If needed, take the filling balls out of the freezer after around 7 minutes and gently re-form with your hands. If the filling was still a little soft when you formed them they may become a little flattened, but once cooler, you can make them into round balls again.
As you get towards the end of the chilling time, melt each of the chocolates separately in small bowls. You can either use a bain Marie/double boiler or melt in intervals in the microwave. Either way, take care to just melt, not warm too long. Prepare a baking sheet/tray with a silicone mat or parchment to place the
Dip half of the filling balls in the white chocolate, and half in the bittersweet/dark chocolate. Dip one at a time in the chocolate, roll or use a spatula, as needed, to coat, then lift out with a fork and rest, tapping edge of bowl, to help allow excess chocolate to drip off. Transfer to the lined baking sheet. Repeat with the other filling balls. If needed, re-freeze the filling balls if they get too soft and re-melt the chocolate if it firms too much.
Once you have dipped all of the fillings, re-melt leftover chocolate (or melt slightly more) to then drizzle over the tops with a small spoon or the fork you used before. Have the cookie crumbs ready to sprinkle on top immediately after you drizzle. I suggest drizzling white on the dark chocolate and vice versa for contrast. Allow to harden then store in a sealed container in the fridge until needed.