Preheat oven to 350 degrees
In the bowl of a stand mixer, or in a large bowl using a handheld mixer, cream together the butter and sugars until light and fluffy (2-3 minutes)
Add in egg and vanilla and mix for another 2 minutes
Add in mashed banana and mix until combined
In a separate bowl, combine flour, oats, cinnamon, baking soda, cloves, and cornstarch
Slowly add the flour mixture into the wet mixture and stir until combined
Stir in raisins until combined
Drop 1-2 tbsp sized balls of dough onto a parchment-lined baking sheet, leaving about 2 inches in between
Bake in preheated oven for 10-12 minutes until the edges of the cookies start to brown lightly
Remove the cookies from the oven, allow them to cool for 5 minutes on the cookie sheet then transfer them to a cooling rack to cool completely