Gypsy Tart Version II - Condensed milk

Sue has made Gypsy Tart using this recipe having tried three times in succession with evaporated milk.  Each time the mix failed to set.  In desperation, and with a deadline looming, she added about a third of a beaten egg. It worked and here's the evidence. But it still wasn't the mousse-y Bird's Butterscotch Instant Whip filling she wanted. Delish tho'.

Serves 12 (or 6 if you’re a sweet-toothed glutton)
Ingredients

• 500g rich shortcrust pastry blind baked in a lined 10 inch wide, 2 inch deep tin (don’t stress, just work with what you’ve got).
• Two 410g tins of condensed milk
• 350g dark muscavado sugar

(and that is it…)
Now for the method behind the madness.

1. Pre-heat oven to 200C/gas 6.
2. Pour the two tins of condensed milk into a large bowl and beat wildly for a couple of minutes with an electric whisk. You want the condensed milk to start to gain in volume.  If you don’t have an electric whisk, then just use a normal whisk and build up a slight sweat. It’s all healthy work.
3. Gradually pour in the muscavado sugar while continuing to whisk. Once all the sugar is combined, continue to whisk for several minutes. The mixture should become a creamy golden brown and have the consistency of quite a thick batter. Something like this picture…
4. Pour this brown creamy mixture into the prepared pastry case and place in the oven. Cook for 25-30 minutes. The surface should be tacky to the touch, and the mixture should seem set if you give the tin a little shake.
5. Allow to completely cool in the tin before serving your gypsy tart up.  Once cool enough, I would advise leaving it in the fridge for an hour or so. As it cools, it shall continue to set.
6. Lightly dust with icing sugar, cut into slices and serve with a dollop of lemony mascarpone (to make this, just stir the zest and juice of half a lemon with about 200g of mascapone).
7. And voilà, fertig, done. Enjoy.