• Preheat the oven to 325°F. Line a baking sheet with parchment paper or a Silpat mat.
• Process the oats in a mini-food processor until it resembles coarse flour. Set aside.

To prepare the cookie dough:

• In a medium bowl combine the sugar and butter. Beat with an electric mixer on high speed until lightened and fluffy. Add the vanilla and milk and blend on low until incorporated.
• In a separate medium bowl combine the AP flour, oat flour, baking soda and salt. Add the dry ingredients to the butter mixture and blend on low until all flour is incorporated.
• Scoop out one teaspoon of cookie dough. Use a small spatula to scrape the dough out of the teaspoon and drop onto the prepared baking sheet. Repeat until the pan is full and all dough mounds are 3-inches apart.
• Roll each dough mound in the palm of your hands to form a ball. Place the dough ball back on the baking sheet at least 3-inches apart. The cookies will spread a lot while baking.
• Bake the cookies for 10 to 13 minutes or until light golden brown around the edges. Allow the cookies to rest for a few minutes before transferring to a wire rack to cool.
• Once cooled match up similar size cookies to make a sandwich before filling.

To prepare the chocolate filling:

• Chop the chocolate into fine shards. In a small glass bowl microwave three-quarters of the chocolate at 50% power until melted.
• Add the remaining chocolate and stir until completely melted. If needed return the chocolate to the microwave for 5 seconds at a time to complete the melting.
• Spread a thick layer of chocolate on the flat side (bottom) of one cookie. Top with another similar sized cookie, flat side down, to make a sandwich. Gently press the cookies together until the chocolate oozes to the outer edge.
• Allow the chocolate to completely set before storing. You can also refrigerate the cookies for 15 minutes or so to speed the process along.