Directions

1. 1

   Preheat your oven to 350°F. Lightly grease a 9×9 inch baking pan with butter or cooking spray. Using a food processor, pulse the rolled oats until they reach a fine powder consistency similar to flour.

2. 2

   In a large mixing bowl, whisk together the oat powder, all-purpose flour, bread flour, dark brown sugar, baking soda, salt, and ground cinnamon until well combined.

3. 3

   Cut the chilled butter into small cubes and add to the flour mixture. Using your fingertips, two knives, or a food processor, work the butter into the dry ingredients until the mixture resembles coarse breadcrumbs.

4. 4

   In a small bowl, whisk together the milk and vanilla extract until combined.

5. 5

   Pour the milk and vanilla mixture into the flour-butter mixture and stir gently with a wooden spoon or fold by hand until just combined. The dough will be quite sticky. If needed, coat your hands lightly with flour to prevent sticking.

6. 6

   Transfer the dough to the prepared baking pan and press it evenly into the bottom, distributing it in an even layer. Bake for 15 to 20 minutes, until a toothpick inserted in the center comes out mostly clean, though the center may still feel slightly tacky to the touch—do not overbake.

7. 7

   Remove the baked base from the oven and allow it to cool to room temperature, then refrigerate for at least 2 to 3 hours until the bars are firm enough to cut and handle.

8. 8

   Once chilled and set, cut the bars into 9 even squares. Top each square with a few pieces of chocolate and one large marshmallow.

9. 9

   Preheat your oven's broiler to high. Place the topped bars on a baking sheet and position under the broiler, about 4 to 6 inches from the heat source. Broil for 2 to 3 minutes, watching carefully and checking frequently until the marshmallows are puffed and just beginning to turn light golden brown. Remove immediately to prevent burning.

10. 10

    Allow the bars to cool for a minute or two before serving. The chocolate will set slightly as they cool.