Step 3: Tell me, what's your flavour?
Now that you have your thick ice cream base, you need to lighten things up a bit! That's where the double cream comes in! By whisking double cream to stiff peaks and folding it into the condensed milk mixture, we will incorporate a lot of air, resulting in a voluminous ice cream "batter' that remains soft enough to scoop. If you are working with 200ml of condensed milk, then you'll need 250ml of double cream. Likewise, if you are using the full 397g tin of condensed milk, you'll need 500ml of double cream (for maths fans, that's a ratio of 4:5 parts condensed milk to double cream).
Before you get to whippin', however, you have another chance to add some more flavours! Chocolate is a particularly good choice here, as you can melt the chocolate into the cream before you whip it to create a ganache. Once chilled, you can then whip that ganache to stiff peaks and use it as you would the plain double cream! Having said that, anything that will dissolve into the double cream, such as extracts, essences and coffee, can be added straight into the cream before whisking and will naturally be evenly distributed as you whip it up!
As explained in the previous section regarding adding flavours, just make sure you don't add anything with too much water content. Not only will this make your ice cream more icy than creamy, but ingredients with a high water content will separate and seep from your cream!