Prepare the coconut whipped cream by opening a can of coconut milk that you've refrigerated overnight. Discard the liquid from the can and place the thick coconut cream into a mixing bowl. Add 1/2 teaspoon vanilla extract and powdered sugar. Whip with a hand mixer until thick. Cover and place in the fridge for an hour.
Preheat the oven to 350°F/180°C and line two baking sheets with silicone baking mats or parchment paper.
In a small bowl, combine the ground flax with the water and mix. Set aside for 5 minutes to thicken.
In a large mixing bowl, combine the plant milk with the vinegar and mix. Set aside for 5 minutes while you prepare the other ingredients.
In a separate mixing bowl, sift together the flour, cocoa, baking powder, and salt.
To the oat milk, add the flax mixture, melted vegan butter, sugar, and 1 teaspoon vanilla. Whisk to combine. Add the dry ingredients to the bowl and gently mix until combined, ensuring there are no lumps. Do not over-mix the batter.
Using a 1 1/2 tbsp cooking scoop, scoop the batter onto the baking sheets about 2 inches apart and bake for 11 minutes or until the tops are dry and not glossy. Allow the cookies to cool slightly before transferring them to a cooling rack to cool completely.
Transfer the coconut whipped cream to a piping bag or ziplock bag and pipe it onto half of the cookies. Pairing them up by size, add a cookie on top of the coconut cream to complete the whoopie pies.
Notes
Use full-fat coconut milk and refrigerate it overnight.Allow the cakes to cool completely before assembling the whoopie pies.