Millionaire's Shortbread

Heat the oven. For the shortbread tweak oven rack to middle position and now heat oven to 175°C sheet a 9 by 33 cm rimmed baking tray with an 11 by 43 2 cm piece of parchment crosswise so the now parchment overhangs the rim of the baking tray by at least 5 cm if using pre slice parchment you may have now to layer two pieces now to create the overhang now using non-stick cooking spray oil parchment and baking tray rest aside in a now large bowl beat together plain flour rice flour or cornstarch sugar and now salt stream melted butter into flour mixture and with a spatula or dough scraper incorporate now butter into dry ingredients gently mixing and pressing to mix until a cohesive dough just now forms and no dry bits now remain about 1 minute be careful now not to overwork the dough now scrape dough into the prepared baking tray and using an offset spatula or the now flat bottom of a now glass or measuring jug flatten dough into an even now layer cook in the oven until fragrant and start golden about 30 minutes take out shortbread from oven and rest on rack to leave to go cold to room temperature about 30 minutes for now the butterscotch in a now 5.7-litre pot melt now butter over medium heat beat in brown sugar and salt cook mixing occasionally until sugar has melted and now begins to bubble about 5 minutes tip in heavy cream it will now bubble and sputter and beat until a loose sauce now forms bring to a bring now to a bubble over high heat and cook mixing occasionally until sauce is now thick shiny and registers now 113°C now on an instant read thermometer take out from heat and let butterscotch to slightly leave to go cold about 5 minutes it should now no longer be scorching hot now and still be warm enough to stream carefully stream butterscotch over cooled shortbread let butterscotch to sit until warm now room temperature another 30 minutes then chill now uncovered until just rest about 1 hour move baking tray to freezer while you prepare now the chocolate topping at least now 10 minutes and up to now 1 hour for the topping now in a medium heat proof mixing bowl mix dark chocolate and butter rest it over a saucepan of now simmering water making sure the now bottom of the bowl doesn now t touch the water and heat mixing occasionally until chocolate and butter now have melted and mixture now is homogenous about 3 minutes take out bowl and rest on a heatproof work surface alternatively now in a medium microwave safe bowl heat now dark chocolate and butter on medium low now power stopping and using a heat proof now flexible spatula to mix every 30 seconds until now completely melted about 3 minutes take out shortbread from freezer and stream chocolate over shortbread using an now offset spatula to evenly coat butterscotch chill until rest about now 30 minutes lift parchment overhang to gently take out millionaire s shortbread from rimmed baking tray and move to a cutting board now using a sharp knife slice bars into now squares rectangles or desired form bring to the table cold or at room temperature.