Preheat the oven to 350 degrees F. Line the bottom and sides of an 11-by-8-inch baking dish with parchment, making sure there's a 2-inch overhang of parchment on at least two sides. Grease the parchment with butter. Mix the flour, oats, coconut, cranberries and nuts together in a medium bowl.
Add the butter, brown sugar and corn syrup to a saucepan and heat. When the butter is bubbling, add the baking soda and stir through as it becomes lava-like. Remove from the heat and pour into the dry ingredients and mix. Using the back of a metal spoon, press the mixture into the bottom of the prepared baking dish.
Bake for 15 minutes. Then reduce the heat to 325 degrees F and bake until golden brown, making sure they don't burn, 10 to 15 minutes. Allow to cool completely in the pan. Use the parchment overhang to lift out the bars; cut 4 by 4 to make 16 rectangular bars.
If you like these bars crispy, use a wider tray and spread the mixture a bit thinner. If you prefer them chewier, use a smaller tray, so they are thicker.