Baked Alaska, at Last

As well as the mis-shapen olive loaves I planned on finally making a proper sized Baked Alaska, at last. I had found a recipe in Rachel Allen's Bake and decided to make the base the night before.
Rachel called it a biscuit base which seemed weird to me as I remember a sponge base from my mothers baked alaska, but I ploughed on thinking Rachel knows better than me.

Ingredients:
For Base:
25g butter
25g caster sugar
1 egg yolk
Half a tsp vanilla extract
60g flour
Pinch baking powder
Meringue:
3 egg whites
Pinch of cream of tartar
200g caster sugar
and 1 litre good quality ice-cream.

Already looking at the ingredients for the base I had my doubts, very small quantities so it won't be very thick, but.... Cream the butter until soft, add the sugar and beat until light and fluffy. Add the egg yolk and vanilla extract and beat until combined. Sift the flour and baking powder and mix until it forms a dough. Put it in clingfilm and put in the fridge for about 30 minutes. I rolled out the dough to the size required, but it's here that my doubts gathered steam. Rachel said to roll it until it was 1cm thick. If I'd done that I would have been making a mini one again so I rolled it to the size I needed and it was about 3mm thick. In fact, it was a biscuit. But looking at the picture in the book the base was definitely thicker. I went ahead and baked it but all the while thinking this can't be right.
After sleeping on it I decided to ditch the thin base and make a sponge, your basic 125g butter/sugar/self-raising flour with 2 eggs and vanilla extract baked for about 20 minutes at 180. That was more like it.
To get the ice cream into a dome shape you leave it out of the freezer to soften and then transfer to a bowl about an inch smaller than your base. Mould it into the dish, smooth the top and pop back in the freezer until you need it.
When you are ready to assemble take the ice cream out of the freezer. Put your base on to a baking tray. Whisk the egg whites until they form soft peaks, add half the sugar and the cream of tartar and whisk until stiff peaks form. Add the rest of the sugar and fold in with a metal spoon. Ease the ice cream on to the base and quickly cover with the meringue making sure you cover right down to the base. Bake in the oven at 220 for about 4 minutes until the meringue is set and pale gold. Serve to expressions of great awe from your guests!