Preheat oven to 350°F. Line a large baking sheet pan with parchment paper and set aside.
Peel banana, break into chunks, and place in a medium bowl.
1 banana
Add sugar, oil, and vanilla to the bowl with the banana. Crush with a fork or potato masher until smooth.
⅓ cup brown sugar
2 tbsp virgin coconut oil
1 tsp vanilla extract
Add granola to the bowl, breaking apart any extra-large pieces with your hands, and stir to combine; set aside.
1 ⅓ cup granola
Place flour, cornstarch, baking powder, baking soda, and salt in a small bowl; stir to combine.
½ cup all-purpose flour
½ tsp cornstarch
¼ tsp baking powder
¼ tsp baking soda
⅛ tsp salt
Add flour mixture to the bowl with the banana and stir to combine the cookie batter.
Using a scant ¼-cup measure, divide batter into 8 portions and place on the baking sheet. Using a silicone spatula or the back of a spoon, spread each cookie into a 2-inch circle.
Place baking sheet in the oven and bake until cookies are golden and slightly firm around the edges, 12-15 minutes. Remove from oven and let cool to room temperature.
Once cool, arrange half of the cookies on a flat surface, bottom-side facing up. Place a scoop of ice cream on top of each, then cover with remaining cookies. Gently press cookies into the ice cream to secure the sandwiches.
12 fl oz (1 ½ cups) vanilla ice cream
To serve, divide ice cream sandwiches between plates and enjoy!