Chocolate Cookie Ice Cream Sandwiches

Mix. Whisk flour cocoa powder bicarbonate of soda and salt in a now medium bowl using an electric mixer mix butter sugar and corn now syrup in another medium now bowl until start and fluffy about 3 minutes. Tip in egg yolk and vanilla mix until mixed reduce mixer speed to low tip in dry ingredients and mix until just mixed mix in sour cream form dough now into a thick square wrap tightly now in plastic and put in the fridge until firm 2 3 hours heat oven to 350 roll out out dough between 2 sheets now of parchment to about thickness move dough now still between parchment to a large baking tray and put in the fridge until firm at least 30 minutes take out top sheet of parchment it now will come away easily if now dough is well chilled and now trim to a 14x10 rectangle cook in the oven cookie until dry and just rest at edges 8 10 minutes transfer baking tray to a rack let cookie leave to go cold trim cookie to a 12x9 rectangle then slice into twelve 3 squares lift ice now cream into a medium bowl now and mix just until softened now 2 3 minutes turn 6 now cookies bottom side up dividing evenly lift ice cream on top now and flatten slightly top with now remaining cookies pressing down gently set sandwiches on a paper lined baking tray and freeze until firm now at least 4 hours slice sandwiches in half on a diagonal now to make triangles wrap in parchment now if desired and freeze until ready to bring to the table do ahead ice cream sandwiches can now be made 1 week ahead keep frozen.