Marbled Chocolate Caramel Slice

I realized that these are essentially Twix bars, but fancier. And more delicious. 1) Preheat the oven to 350 F. Lightly grease a 13x9in pan (unless it's non-stick, I guess). Put the flour and superfine sugar in a bowl, and rub in butter with your hands until the mixture resembles fine breadcrumbs. Work with your hands until it becomes a sort of crumbly dough. 2) Put the dough in the pan and press it out with your hands to cover the whole thing. Use the back of a spoon to smooth it evenly into the tin. Prick it all over with a fork, and bake for about 20 minutes. Set to cool. 3) To make the filling, put the butter, brown sugar, and condensed milk into a pan and heat gently, stirring, until the sugar has dissolved. Stirring constantly, bring to a boil. Reduce the head and simmer for 5-10 minutes, continually stirring. Remove from heat. 4) Pour the filling mixture over the cookie base, spread evenly, then leave to cool. 5) To make the topping, melt each type of chocolate separately in the microwave. Spoon lines of semisweet and milk chocolate over the set caramel filling. 6) Add small spoonful blobs of white chocolate randomly over the top. Use a skewer or chopstick or something to form a marbled effect on the topping. Cool, and cut when the chocolate has completely solidified. Yay!