Gluten free key lime pie

I wanted a gluten free dessert for an Easter family gathering and came across this recipe.  It wasn't gluten free when I found it, but with a small adaptation it could be and it was also easy to make.

Ingredients

For the base

• 350g gluten free digestive biscuits (gluten free digestives are sold in Tesco and Sainsbury but if you don't have an allergy/intolerance to gluten then just use normal digestives)
• 125g unsalted butter

For the filling

• 4 large eggs, separated
• 400ml full fat condensed milk (I used low fat)
• Finely grated zest and juice of 4 limes
• 50g golden caster sugar (I used normal granulated)

Method

• Preheat oven to 160°C (fan oven) and grease a deep 25cm fluted tart tin with a loose bottom.  I don't think my tart tin was very deep and it would have been better if it had been deeper.  This is the one I used.
• To make the base crush the biscuits either in a bag using a rolling pin or using a food processor.
• Melt the butter and mix with the biscuit crumbs.  When I did this I lacked faith and panicked and added more butter.  Don't do what I did.  Have faith and follow the recipe.
• Press the biscuit and butter mixture into the greased tin on the base and up the sides to make the pie case.  If you don't have a tart tin then you can use a springform tin instead but it won't look quite as pretty.
• Bake the case in the oven for 10-15 minutes.  My case shrank in the oven and I nearly threw the thing in the bin.  I think that might have been because I messed with the recipe and added too much butter.  But just in case your case shrinks too, then just make up a little extra biscuit and butter mix and do a DIY fix up job where it shrank (but don't re-bake the case).  This might not matter if you have a very deep tart tin but if you don't then you will need the sides of the case to be as tall as possible to contain the filling.
• For the filling, beat the egg yolks until they are light and fluffy and then beat in the condensed milk, lime zest and juice.
• In another bowl, whisk the egg whites and sugar until firm.
• Gently fold the egg whites into the lime mixture using a large metal spoon.
• Fill the biscuit base with the lime mixture and bake in the oven for 20-25 minutes until set and slightly browned around the edges.  When I filled my base I had a little bit too much filling for the size of my base.  I also had a bit extra base mix after my DIY fix it job on the base.  I used the extra biscuit base in a couple of ramekins and baked for a few minutes and then added the spare filling thus making two extra mini desserts.  Also, when baking the main pie I saw that one edge of the pie went a light brown colour quite quickly so I spent the whole of the baking time gradually turning the pie in the oven so it cooked evenly.
• Once out of the oven, the pie, not you, leave to cool.  The pie will shrink a bit so don't worry this is normal.
• I remove from the tin by putting the tin on a bowl and gradually removing the edge of the tart tin downwards allowing me to lift the pie away from the edge bit of the tin.  I've not been brave enough to remove from the base of the tin.  That just seemed like a disaster waiting to happen.
• Just before serving, dust the pie lightly with icing sugar.  You could go the whole hog and do fancy decoration with lime slices and mint leaves like the person who wrote the recipe in the first place, like this. Or not.