Preheat oven to 350°F (180°C) and lightly grease a muffin pan. I recommend using a silicon one.
In a small bowl, combine the oat flour, almond flour, and tapioca starch. Add the maple syrup, almond milk, and vanilla extract. Mix until combined. The batter will be quite thick, set aside.
In another bowl, beat the aquafaba using a hand mixer until it forms soft peaks. This step can take up to 5 minutes.
Add the thick batter to the aquafaba and carefully mix using a spatula until well combined. Stop as soon as the aquafaba is integrated. You should get a light and fluffy batter.
Divide the batter (about 2 tbsp per cavity) into the 6 cavities of the muffin pan and bake for 25 minutes.
Remove from the oven but don't turn it off, lower the oven to 300°F. While the cookies are still warm, use the top of a bottle to make an indentation in the center of each cookie. A small jar or pill bottle can also work.
Let the cookies cool 5 minutes and carefully remove from the pan. Place the cookie cups on a baking sheet lined with parchment paper and bake for another 8-10 minutes. This step makes the cookie a bit crispier on the outside.
Remove from the oven and let cool completely. In the meantime, prepare the filling(s). You don't have to make them all, just pick your favorite one!
Cookies are best served the same day but will keep for up to 3 days in an airtight container at room temperature.