A couple tips: Adding a teaspoon of oil to the melted chocolate makes it more manageable. Also, if the first layer gets too firm when chilling, the second layer does not adhere. I find that carefully adding the second layer when the white chocolate is chilled but not quite firm solves this problem. If the first layer has gotten too firm putting it in a warm over for about half a minute will soften it. A bit of the white might mix in with the semi-sweet layer but it actually looks quite fine!
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