Make the Graham Cracker Dough: Preheat the oven to 350°F (180°C) and line an 8-inch (20 cm) square pan with parchment paper. Set aside.
In a medium bowl, combine the flour, brown sugar, cinnamon, baking soda and salt together.
With a pastry blender or using your fingers, rub the butter into the flour mixture until it resembles coarse breadcrumbs.
In a small jug, whisk the honey, milk and vanilla extract together, then pour into the flour mixture and combine until you have a soft, sticky dough. You can use it straight away or keep it in the fridge for up to 3 days.
Assemble the Smores Bar: Evenly press about ¾ of the Graham cracker dough into the bottom of the prepared pan, reserving the rest.
Spread the marshmallow fluff over the top of the dough all the way to the edges.
Sprinkle the chocolate chunks over the fluff, then crumble the remaining ¼ dough over the chocolate. The dough will spread out as it bakes.
Bake for about 35 minutes, until the Graham cracker dough has browned. (It will still be jiggly in the middle slightly.)
Let cool completely before cutting into 9 squares.
Enjoy straight away and store leftovers at room temperature in an airtight container for up to 3 days.