Half a packet of Tesco Value Ginger Nuts (150g)
2 ounces butter (I used Tesco own brand salted, that's about 1/5th a pack).
1 ounce brown sugar (any will do, recipe calls for demerara, I used light brown baking sugar).
4/5ths a pack of Tesco Full Fat soft cheese (about 175g)
150 ml double cream (I used some cheap stuff)
1 tin condensed milk (again, one of the cheap brands is fine)
Zest and juice of 4 limes
And yes, I know I mixed imperial and metric in the ingredients list, it's fine.
You also need a 23cm cake tin or flan tin, I used a Sainsbury Cook's Collection springform thing I got in a sale awhileback, the Cook's Collection stuff is REALLY good but pricey, they put it on sale fairly regularly, buy what you can afford when they do, seriously. From experience, line the base of the tin with a bit of overlap, I didn't do this hence you're not getting a picture.
Crush the biscuits in a bag using a rolling pin or similar—an empty cereal bag is perfect for this, cheap thin plastic bags not so much, but I managed to avoid spilling too much…
Melt the butter over a low heat in a medium pan, once all melted remove from heat, mix in the sugar and the biscuit crumbs—note, don't do this in a milk pan, it's not big enough and you'll spill stuff (note the trend here). Once mixed in you'll have a nearly solid mix, push that into the base of the tin and put it in the fridge.
Next up, put the cheese, cream and condensed milk into your mixing bowl with the lime zest (but not the juice, yet). I heartily recommend an electric whick or mixer for the next bit, I bought a cheap one from Wilko last year and it's So Much Easier. Whisk all this together and keep whisking for a bit. Slowly start adding in the juice in small amounts, keep whisking. It'll start to thicken, for me it started to really thicken after the juice started being added so be careful from now on, miss_s_b tells me the acid in the juice reacts with the cream to thicken. Keep going, slowly adding the juice, until the mixture is very thick.
Now, pour, prod and spoon the cream mixture into the tin on top of the biscuit base. Try to get as much in as possible and resist the temptation to taste too much (I almost managed this bit). Put in the fridge to set, it'll take at least 3 hours in the fridge, probably more, overnight is best. Don't be tempted to take it out before set, it'll make a mess.
You can, if you want, put some whipped cream on top, top with strawberrys, etc, but I didn't bother, it didn't need it. Total cost about £4 depending on ingredient quality, plus £30ish of equipment, you could do it with a hand whisk but, um, you'll need strong whisking muscles.