You will need:
10-12 small glass ramekins (you can buy these in department stores, I use the ones that come with Gu Puds, we've got about 30)
For the base:
1 200g(ish) box fine milled oatcakes (I use Nairns which is 218g, I don't personally need to worry about buying the guaranteed gluten free ones which are more expensive, these are made in a factory that also makes gluten products)
125g unsalted butter
some sugar: I recommend a couple teaspoons of molasses sugar with the lumps broken up as best as possible and a couple teaspoons caster sugar.
For the topping:
one 250g tub ricotta cheese
100g white chocolate (I've tried other chocolates, it tends to not work, plus miss_s_b can eat white chocolate without risk of dying, which is good). I recommend Sainsbury Belgian Cooking Chocolate for cost/benefit quality wise
Either 2 limes, zest and juice, with 2-4 teaspoons of ground ginger for taste (I think 4 is too much, others disagree)
or one large orange, zest and juice, 1-2 teaspoons cinnamon, 1-2 teaspoons nutmeg
You could almost certainly try other fruit+spice combos, this is what I've done, successfully, so far.
First, make the base: crush the biscuits as much as possible, you want breadcrumb style crumbs. Melt the butter in the microwave, careful not to overheat it. Mix the butter and the sugars thoroughly through the crushed biscuits, you should end up with a very loose, crumbly dough. NB: You can use 200g of any biscuits for this, including standard sweet digestives, but if you use sweet biscuits omit the extra sugar.
Share the mix out amongst the ramekins and press it into the bases, you'll likely get just over 1cm depth per tub, don't worry about exactness here. Put them in the fridge to cool.
Whisk the ricotta in a glass bowl. Using a different glass bowl, break the chocolate up and carefully melt in the microwave, if you're not used to doing this, full power for 30 seconds, bring out stir thoroughly, repeat until it's all just melted, be careful not to over melt as the chocolate can crystallise or otherwise stop being nice.
Whisk the melted chocolate into the ricotta. Then whisk in the flavourings. Share the topping mix about the ramekins, you'll find the lime is a fairly tough mix, you might want to add some more lime juice to soften it further, the orange will likely be a fairly loose mix depending on size and juiciness of orange. Try to press the mix down and spread it out.
Put back into fridge to chill for a minimum of 2 hours (the topping really does need to set). Serve and enjoy.
I am grateful to hollymath and A_C_McGregor for their assistance putting the ingredients together yesterday and their, um, help in choosing the spice quantities—I suspect both would've happily put even more ginger in, but I think 4 teaspoons is too much.