Line a freezer-safe plate with waxed paper. Place banana slices on the plate and cover with plastic wrap. Freeze until solid, about 2 hours.
Fill a small bowl with hot water. Transfer 1/4 cup frozen banana slices to a resealable plastic bag and seal tightly. Place bag into the bowl of hot water and let sit until bananas are melted, 5 to 10 minutes.
Stir milk and vinegar together in a bowl to create buttermilk. Set aside for 5 minutes.
Mix flour, sugar, baking powder, baking soda, and salt together in a large bowl.
Whisk egg, butter, coconut extract, and banana extract into the bowl with the buttermilk mixture. Mix buttermilk-egg mixture into the bowl with the flour mixture and stir batter until smooth. Slowly pour melted bananas into batter and stir until smooth.
Coat a medium-sized skillet with cooking spray and heat over medium heat. Pour batter by tablespoonfuls onto the skillet to create mini pancakes. Wait for pancakes to bubble, about 1 minute, then flip. Cook 1 minute more and transfer pancakes to a plate. Repeat with remaining batter.