Start by melting either the white or dark chocolate—whichever you want to be the base of the bark(I started with the white)—in a microwave or over a double boiler. Melt until completely smooth.
Lay the chocolate out in a thin layer on a non-stick surface like wax paper.
Melt the other chocolate and carefully spread it on top of the first layer, gently swirling the two together with a utensil.
Sprinkle on the Crasins and the walnuts all over the chocolate and press them in lightly with your hand.
Freeze the chocolate for about 20 minutes until it has completely hardened.
With a sharp knife, cut the chocolate into unequal pieces. Store for up to 2 weeks.