Make the cookie. Preheat the oven to 375°F. Line a circular baking sheet with parchment paper.
In a large bowl mix the maple syrup, cashew butter, date sugar, 2 tablespoons of the oat milk, ground flaxseeds, and vanilla extract.
Add in the oat flour, baking soda, and salt. Stir until a dough forms, adding an additional tablespoon or two of milk if necessary.
Place on the baking pan and flatten into a circle.
Bake for 10-12 minutes until the cookie is slightly golden. Let the cookie cool 1-2 minutes before transferring it from the pan to a wire rack. Let the cookie cool completely.
Make the frosting. Beat the frosting ingredients in a medium bowl using a stand mixer, hand mixer, or (if you’re feeling strong) a fork. Place the frosting in the fridge until ready to assemble.
Assemble. When the cookie is completely cool, spread the frosting in an even layer over the cookie, leaving ½" of space around the edges.
Decorate with fruit as desired. Slice, serve, and enjoy!