Preheat the oven to 180°C/ 160°C fan/ gas mark 4/ 350°F
Lightly grease the tin with butter, optionally lining the base with baking parchment or magic liner
For the shortbread:
Mix the butter, sugar and flour. Use any sort of mixer or food processor
Combine with your hands to make a smooth ball of dough
Press into the tin with your fingers. Use the edge of an upside-down spoon to pull the edges of the dough level
Cook for 20-25 minutes until pale golden brown
Put the tin on a cooling rack.
For the caramel (while the shortbread is cooking):
Weigh the butter, sugar and golden syrup into a saucepan. Melt on a low-medium heat
When melted, add the condensed milk and bring to the boil. Boil steadily for 5-8 minutes, stirring all the time, until the caramel has thickened and turned a golden colourDon't have the heat too high or it will burn (see tip)
Remove from the heat and pour over the shortbread base
Leave to cool for 30-60 minutes.
For the chocolate topping:
Melt the chocolate. Put the chocolate in a small basin andEITHER melt in the microwave on 30-sec burstsOR Put the basin over a saucepan of hot water. Don't let the water boil or touch the bowl. Keep stirringFor step-by-step instructions see How to Melt Chocolate
When the chocolate has melted, pour over the base and spread evenly using a knife.
Leave to cool. Refrigerate if necessary, but see tip
Use a sharp knife dipped in hot water to cut into squares or fingers as you prefer
Don't try to cut it straight from the fridge - the chocolate will crack.
Notes
Everyday Cooks tips:
To measure golden syrup, put the tin on your scales and set to 0. Spoon out the syrup until the scale reads -100g. Use the spoon to stir the ingredients in the pan. The syrup will melt off. (If you have balance scales, I'm afraid you have to do the mental arithmetic)
If the caramel catches on the bottom of the pan you can rescue it by taking another saucepan and pouring the caramel in, avoiding scraping the bottom where it's burnt. If it isn't too bad, ignore it. It'll taste fine
If you refrigerate Millionaires Shortbread the chocolate will go dull. It tastes fine but if it's for a special occasion, leave it out of the fridge
Storage:Millionaires Shortbread keeps for at least a week in an airtight container, longer if it's in the fridge - but see tip above