1. Make the butterscotch sauce first to give it plenty of time to cool. Pour the Lyle's Golden Syrup, the butter and the Tate & Lyle Light Soft Brown Sugar together in a small pan. Slowly dissolve the sugar over a low heat for about 6-8 minutes, stirring occasionally. Once the sugar has dissolved, increase the heat slightly and cook for a further 5 minutes. Slowly add the cream and cook for another 5 minutes until reduced. If you have a sugar thermometer, you want the butterscotch to reach about 107°C (225°F) to make sure the sauce is thick enough. Remember your sauce will thicken quite a bit as it cools down. Take off the heat and leave to cool completely.
2. Preheat the oven to 175°C/160° Fan, 325°F, Gas 3.
3. Place the butter, Lyle's Golden Syrup and Tate & Lyle caster sugar in a bowl or a stand mixer and whisk until soft and creamy. Lightly beat the eggs and drizzle them into the mixture a little at a time, making sure each batch is well combined before adding more.
4. Sift over the flour and lightly fold it into the mixture and then add the milk to make a soft consistency (so it easily drops from the spoon). Don’t over mix once the flour is added so you don’t build up the gluten. Spoon the mixture into a brownie tin 20cm (8”) x 30cm (12”) greased and lined with parchment paper. Bake on the middle shelf for 30-35 minutes until gorgeously golden brown, and a skewer comes out clean when poked into the middle of the cake. Take out of the oven, leave in the tin for 5 minutes and then turn out onto a wire rack to cool completely.
5. Once the cake has cooled, poke holes about 2-3cm apart with the end of a wooden spoon. Fill a piping bag with the butterscotch sauce and fill the holes liberally right to the top.
6. To make the frosting, place all of the ingredients into a large bowl and whisk until stiff. You might want to mix in the mascarpone a bit first to avoid splatter! Be careful not to over whip and curdle the mixture.
7. Separate out about ¼ of the frosting for the decoration and spread the rest evenly on top of the cake.
8. Of the ¼ set aside, colour about 2/3 of it red and the other 1/3 blue. You’ll need quite a bit to give it a vivid colour.
9. Using a knife or cocktail stick, mark out the lines of the union jack to follow with your piping. Pipe the large red cross first, using a wide piping nozzle, followed by the smaller red diagonal lines. Then fill the small triangles in blue.
10. This cake is best eaten immediately, but if not, it should be stored in the fridge due to the dairy topping. Eat within 3 days.