Start by combining the milk and vinegar in a small bowl and let it sit for 5-10 minutes to curdle into a buttermilk substitute—this acidic ingredient is crucial for activating the baking soda and creating the signature tangy red velvet flavor. While the buttermilk develops, whisk together the gluten-free flour, cocoa powder, baking soda, kosher salt, and espresso powder in a separate bowl. The espresso powder deepens the chocolate notes without adding coffee flavor, so don't skip it. Set both mixtures aside until you're ready to build the dough.

In a small bowl, combine the cornstarch and water to create a slurry, which will help bind the gluten-free dough and give these cookies a better texture. Set aside. I find that this simple cornstarch slurry makes a huge difference in preventing the gluten-free cookies from becoming too crumbly or dense, so it's worth the extra step.

Beat the room-temperature butter and dark brown sugar together for 2-3 minutes until light and fluffy, which incorporates air for a better cookie texture. Add the cornstarch slurry from Step 2, the curdled buttermilk from Step 1, molasses, vanilla extract, and red food coloring, mixing until fully combined. The molasses adds depth and moisture to balance the cocoa, while the red coloring gives you that classic red velvet hue. Gently fold in the dry ingredient mixture from Step 1 until just combined—don't overmix, as this can toughen the dough. Finally, stir in the semi-sweet chocolate chips and the roughly crushed cookie pieces (the 5 GF chocolate cookies), distributing them evenly throughout.

Transfer the dough to the refrigerator and chill for 2.5 hours. This resting time allows the flour to fully hydrate, the flavors to meld, and the dough to firm up, which helps the cookies hold their shape during baking and prevents excessive spreading. Don't skip this step—it's essential for gluten-free baking success.

Preheat your oven to 325°F. Once the dough has chilled, scoop it into 12 evenly sized balls (about 2 tablespoons each) and place them on a parchment-lined baking sheet, spacing them about 4 inches apart since they'll spread during baking. Press the tops of each dough ball into the Ghirardelli 60% cacao chocolate chips so they adhere to the surface—this creates a professional appearance and ensures each bite has chocolate.

Bake at 325°F for 13-15 minutes—the cookies should be set around the edges but still slightly soft in the center. Remove from the oven and immediately press 9 GF chocolate cookies (Glutino brand) into the tops of the warm cookies, pressing gently so they adhere without cracking the cookie. I like to do this while the cookies are still warm because the residual heat softens the surface just enough for the cookie chunks to stick without sinking too deep. Let the cookies cool on the baking sheet for 5 minutes to set slightly before transferring to a wire rack to cool completely.