Heat the oven to 200°C/180°C fan/ gas mark 6. Grease and line with baking parchment a 20cm/ 9inch square, loose bottomed brownie tin.
In a large bowl mix in the flour, golden caster sugar, cornflour and ground ginger. Slice the vegan butter into cubes and add to the bowl. Use your fingertips to rub the butter into the flour until the mixture is well combined and forms large clumps. Pour out into the prepared tin and press the mixture down to form an even layer.
Poke a fork throughout the shortbread, then place in the oven for 30 minutes. The shortbread should be golden brown and firm to touch. Remove from the oven and leave to cool in the tin.
Next, add the vegan condensed milk, vegan butter and sugar to a large saucepan. Bring to a gentle simmer. When the butter has melted, Increase the heat and bring the mixture to a hard rolling boil. Reduce the heat to medium and continue to heat the caramel for 5-7 minutes, stirring continuously.
You can turn off the heat when the sugar thermometer reads 116°C. If you don't have a thermometer to hand, the caramel is ready when it is copper in colour and has thickened. Then stir in the orange extract, orange zest and salt. Pour the caramel over the shortbread and leave to cool for 10 minutes in the tin. Then place in the fridge to set for approximately 1.5-2hrs.
To make the chocolate topping, add the chocolate and oil to a bain-marie or heatproof bowl placed over a simmering bowl of hot water. Melt the chocolate and coconut oil until silky smooth. Then immediately pour over the set caramel. Leave to set in the fridge for 1 hour.
To serve, remove the tin from the loose bottom. Cut into 16 squares or if you want to savour your Millionaire’s Shortbread, slice into 25 squares. Decorate each square with flaky sea salt.