Around 20 mins after putting the bowl in the freezer, remove the chocolate ice cream from the freezer. Leave at room temperature for about 10 mins. Meanwhile, melt half the dark mint chocolate in a heatproof bowl over a pan of simmering water, ensuring the bowl doesn’t touch the water (or do this in the microwave in 10-second bursts), stirring until smooth. Once the mint chocolate chip ice cream has set (it’s fine if it’s still slightly soft), drizzle over the melted dark mint chocolate – it should set almost as soon as it touches the ice cream. Next, layer in the chocolate ice cream, ensuring it's in as even a layer as possible. Freeze again for another 30-45 mins to set.