Millionaire Shortbread [Low Fat]

What's that? Low fat food tastes of nothing, you say? Make this Millionaire Shortbread and get back to me.
As I mentioned in January's Baking With Spirit challenge, Cake Of The Week is having a Low Fat January. I personally find it too hard to swerve away from sugar entirely, even when I'm trying to eat well. Making cakes and other baked goods low in fat (and not balancing it out with sugar, as food manufacturers have been criticised for doing) means I can have something sweet every now and then (read: once a day) whilst not shaming myself for ruining my hard work. Every recipe posted this month will be low fat, and you can find tips on healthier baking here. With these recipes, low fat does not equate to low taste.
This Low Fat Millionaire Shortbread is adapted from the Roxanne's Millionaire's Shortbread in Nigella Lawson's How To Be A Domestic Goddess. I ran out of low fat spread so I used a 50/50 mixture of low fat spread and low fat mayonnaise in the caramel (see these brownies before you scoff at the thought of using mayonnaise in baking). It worked really well and you'd never know I hadn't used butter. The only I problem I have with this recipe is the need to exercise patience and wait for everything to set before diving in.

Makes 12
Ingredients

For the shortbread

• 225g Plain Flour
• 75g Caster Sugar
• 175g Low Fat Spread

For the topping

• 100g Low Fat Spread
• 100g Light Mayonnaise
• 397g Can Light Sweetened Condensed Milk
• 4 Tbsp Golden Syrup
• 325g Dark Chocolate

Method

• Preheat the oven to 170C/160C fan and line a brownie tin with baking parchment.
• Make the shortbread by placing the flour, sugar and spread into a mixing bowl and rubbing together. The dough should start to clump together but will still be slightly crumbly.
• Press the dough into the bottom of your brownie tin, then prick all over with a fork.
• Place in the oven and bake for five minutes, then turn the oven down to 150C/140C fan and bake for a further 30 minutes. Leave the shortbread in the tin to cool.
• Make the caramel by first melting the spread and mayonnaise in a microwaveable bowl in the microwave.
• Next, pour the light sweetened condensed milk into the bowl with the melted spread and mayonnaise and add the golden syrup.
• Stir well, then microwave for 6-8 minutes, stirring after each minute. At the end, the caramel should be bubbling and darker in color than at the beginning.
• Pour the caramel over the top of the shortbread and allow to cool and set.
• Break the chocolate into chunks then melt in the microwave (this should take 1-2 mins, but check every 30 seconds). Pour the chocolate over the top of the caramel and leave to set. 
• To neatly cut the shortbread into slices, put the sharp end of a knife into a mug of hot water for a couple of minutes beforehand.